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https://github.com/renatoGarcia/icecream-cpp
🍦 Never use cout/printf to debug again
https://github.com/renatoGarcia/icecream-cpp
cpp cpp11 cpp14 cpp17 debug debugging debugging-tool header-only print single-header-lib
Last synced: 2 days ago
JSON representation
🍦 Never use cout/printf to debug again
- Host: GitHub
- URL: https://github.com/renatoGarcia/icecream-cpp
- Owner: renatoGarcia
- License: other
- Created: 2019-02-03T15:49:38.000Z (almost 6 years ago)
- Default Branch: master
- Last Pushed: 2024-04-05T00:30:17.000Z (10 months ago)
- Last Synced: 2024-04-05T01:52:35.576Z (10 months ago)
- Topics: cpp, cpp11, cpp14, cpp17, debug, debugging, debugging-tool, header-only, print, single-header-lib
- Language: C++
- Homepage:
- Size: 481 KB
- Stars: 522
- Watchers: 11
- Forks: 30
- Open Issues: 10
-
Metadata Files:
- Readme: README.md
- License: LICENSE.txt
- Authors: AUTHORS
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README
# IceCream-Cpp
[![CI.badge]][CI.link]
[![LICENSE.badge]][LICENSE.link]
IceCream-Cpp is a little (single header) library to help with the print debugging in C++11
and forward.
[Try it at Compiler Explorer!](https://godbolt.org/z/WKbxejjaa)
**Contents**
* [Install](#install)
* [Nix](#nix)
* [Conan](#conan)
* [Usage](#usage)
* [Direct printing](#direct-printing)
* [Range views pipeline](#range-views-pipeline)
* [Return value and IceCream apply macro](#return-value-and-icecream-apply-macro)
* [Output formatting](#output-formatting)
* [Character Encoding](#character-encoding)
* [Configuration](#configuration)
* [enable/disable](#enabledisable)
* [output](#output)
* [prefix](#prefix)
* [show_c_string](#show_c_string)
* [wide_string_transcoder](#wide_string_transcoder)
* [unicode_transcoder](#unicode_transcoder)
* [output_transcoder](#output_transcoder)
* [line_wrap_width](#line_wrap_width)
* [include_context](#include_context)
* [context_delimiter](#context_delimiter)
* [Printing strategies](#printing-strategies)
* [C strings](#c-strings)
* [Wide strings](#wide-strings)
* [Unicode strings](#unicode-strings)
* [Streamable types](#streamable-types)
* [Pointer like types](#pointer-like-types)
* [Range types](#range-types)
* [Tuple like types](#tuple-like-types)
* [Optional types](#optional-types)
* [Variant types](#variant-types)
* [Exception types](#exception-types)
* [Not streamable types](#not-streamable-types-clang-only)
* [Pitfalls](#pitfalls)
With IceCream, an execution inspection:
```c++
auto my_function(int i, double d) -> void
{
std::cout << "1" << std::endl;
if (condition)
std::cout << "2" << std::endl;
else
std::cout << "3" << std::endl;
}
```
can be coded instead:
```c++
auto my_function(int i, double d) -> void
{
IC();
if (condition)
IC();
else
IC();
}
```
and will print something like:
ic| test.cpp:34 in "void my_function(int, double)"
ic| test.cpp:36 in "void my_function(int, double)"
Also, any variable inspection like:
```c++
std::cout << "a: " << a
<< ", b: " << b
<< ", sum(a, b): " << sum(a, b)
<< std::endl;
```
can be simplified to:
```c++
IC(a, b, sum(a, b));
```
and will print:
ic| a: 7, b: 2, sum(a, b): 9
We also can inspect the data flowing through a range views pipeline (both [STL
ranges](https://en.cppreference.com/w/cpp/header/ranges) and
[Range-v3](https://ericniebler.github.io/range-v3/)), by inserting a `IC_V()` function at the
point of interest:
```c++
auto rv = std::vector{1, 0, 2, 3, 0, 4, 5}
| vws::split(0)
| IC_V()
| vws::enumerate;
```
So that when we iterate on `rv`, we will see the printing:
ic| range_view_63:16[0]: [1]
ic| range_view_63:16[1]: [2, 3]
ic| range_view_63:16[2]: [4, 5]
This library is inspired by the original [Python IceCream](https://github.com/gruns/icecream) library.
## Install
The IceCream-Cpp is a one file, header only library, having the STL as its only
dependency. The most immediate way to use it is just copy the `icecream.hpp` header into
your project.
To properly install it system wide, together with the CMake project files, run these
commands in IceCream-Cpp project root directory:
```Shell
mkdir build
cd build
cmake ..
cmake --install .
```
### Nix
If using [Nix](https://nixos.org), IceCream-Cpp can be included as a flakes input as
```Nix
inputs.icecream-cpp.url = "github:renatoGarcia/icecream-cpp";
```
The IceCream-Cpp flake defines an overlay, so that it can be used when importing `nixpkgs`:
```Nix
import nixpkgs {
system = "x86_64-linux";
overlays = [
icecream-cpp.overlays.default
];
}
```
Doing this, an `icecream-cpp` derivation will be added to the `nixpkgs` attribute set.
A working example of how to use IceCream-Cpp in a flake project is [here](example_project/flake.nix).
### Conan
The released versions are available on [Conan](https://conan.io) too:
```Shell
conan install icecream-cpp/0.3.1@
```
## Usage
If using CMake:
```CMake
find_package(IcecreamCpp)
include_directories(${IcecreamCpp_INCLUDE_DIRS})
```
will add the installed directory within the include paths list.
After including the `icecream.hpp` header in a source file:
```C++
#include
```
all the functionalities of IceCream-Cpp library will be available by the functions
[`IC`](#direct-printing), [`IC_A`](#return-value-and-icecream-apply-macro), and
[`IC_V`](#range-views-pipeline); together with its respective counterparts `IC_F`,
`IC_FA`, and `IC_FV`; that behave the same but accept an [output formatting
string](#output-formatting) as its first argument.
### Direct printing
The `IC` is the simplest of the IceCream functions. If called with no arguments it will
print the [prefix](#prefix), the source file name, the current line number, and the
current function signature. The code:
```C++
auto my_function(int foo, double bar) -> void
{
// ...
IC();
// ...
}
```
will print:
ic| test.cpp:34 in "void my_function(int, double)"
If called with arguments it will print the [prefix](#prefix), those arguments names, and
its values. The code:
```C++
auto v0 = std::vector{1, 2, 3};
auto s0 = std::string{"bla"};
IC(v0, s0, 3.14);
```
will print:
ic| v0: [1, 2, 3], s0: "bla", 3.14: 3.14
The variant `IC_F` behaves the same as the `IC` function, but accepts an [output
formatting string](#output-formatting) as its first argument.
### Range views pipeline
To print the data flowing through a range views pipeline (both [STL
ranges](https://en.cppreference.com/w/cpp/header/ranges) and
[Range-v3](https://ericniebler.github.io/range-v3/)), we use the `IC_V` function, which
will print any input it receives from the previous view. Since the `IC_V` function is
within a range views pipeline, the printing will be done lazily, while each element is
generated. For instance:
```C++
namespace vws = std::views;
auto v0 = vws::iota('a') | vws::enumerate | IC_V() | vws::take(3);
for (auto e : v0)
{
//...
}
```
In this code nothing will be printed when `v0` is created, just when iterating over it. At
each iteration in the `for` loop one line will be printed, until we have the output:
ic| range_view_61:53[0]: (0, 'a')
ic| range_view_61:53[1]: (1, 'b')
ic| range_view_61:53[2]: (2, 'c')
> [!NOTE]
> The Icecream-cpp will search the current scope trying to detect any "#included" range-v3
> header. If any is dectected, the support to range-v3 will be automatically enabled.
> While convenient, that requires that the Icecream-cpp header be included at a line below
> some range-v3 header. To make sure that the support to range-v3 is enabled regardless of
> that header detection, you can define a macro `ICECREAM_RANGE_V3` before including the
> `icecream.hpp` header
The `IC_V` function has two optional parameters, `IC_V(name, projection)`.
#### name
The variable name used to the view when printing. The printing layout is: `[]:
`. If the name parameter is not used, the default value to `` is
`range_view_`.
The code:
```C++
vws::iota('a') | vws::enumerate | IC_V("foo") | vws::take(2);
```
when iterated over will print:
ic| foo[0]: (0, 'a')
ic| foo[1]: (1, 'b')
#### projection
A [callable](https://en.cppreference.com/w/cpp/named_req/Callable) that will receive as
input the elements from the previous view and must return the actual object to be printed.
The code:
```C++
vws::iota('a') | vws::enumerate | IC_V([](auto e){return std::get<1>(e);}) | vws::take(2);
```
when iterated over will print:
ic| range_view_61:53[0]: 'a'
ic| range_view_61:53[1]: 'b'
> [!NOTE]
> The `IC_V` function will still forward to the next view an unchanged input element,
> exactly as it was received from the previous view. None action done by the `projection`
> function will have any effect on that.
The variant `IC_FV` has the same behavior as the `IC_V` function, but accepts an [output
formatting string](#output-formatting) as its first argument.
### Return value and IceCream apply macro
Except when called with exactly one argument, the [`IC`](#direct-printing) function will
return a tuple with all its input arguments. If called with one argument it will return
the argument itself.
This is done this way so that you can use `IC` to inspect a function argument at calling
point, with no further code change. In the code:
```C++
my_function(IC(MyClass{}));
```
the `MyClass` object will be forwarded to `my_function` exactly the same as if the
`IC` function was not there. The `my_function` will continue receiving a rvalue reference to a
`MyClass` object.
This approach however is not so practical when the function has many arguments. On the code:
```C++
my_function(IC(a), IC(b), IC(c), IC(d));
```
besides writing four times the `IC` function, the printed output will be split in four
distinct lines. Something like:
ic| a: 1
ic| b: 2
ic| c: 3
ic| d: 4
Unfortunately, just wrapping all the four arguments in a single `IC` call will not work
too. The returned value will be a `std:::tuple` with `(a, b, c, d)` and the `my_function`
expects four arguments.
To work around that, there is the `IC_A` function. `IC_A` behaves exactly like the `IC`
function, but receives a [callable](https://en.cppreference.com/w/cpp/named_req/Callable)
as its first argument, and will call it using all the next arguments, printing all of them
before that. That previous example code could be rewritten as:
```C++
IC_A(my_function, a, b, c, d);
```
and this time it will print:
ic| a: 1, b: 2, c: 3, d: 4
The `IC_A` function will return the same value as returned by the callable. The code:
```C++
auto mc = std::make_unique();
auto r = IC_A(mc->my_function, a, b);
```
behaves exactly the same as:
```C++
auto mc = std::make_unique();
auto r = mc->my_function(a, b);
```
but will print the values of `a` and `b`.
The variant `IC_FA` behaves the same as the `IC_A` function, but accepts an [output
formatting string](#output-formatting) as its first argument, even before the callable
argument.
### Output formatting
It is possible to configure how the value must be formatted while printing. The following code:
```C++
auto a = int{42};
auto b = int{20};
IC_F("#X", a, b);
```
will print:
ic| a: 0X2A, b: 0X14
when using the `IC_F` variant instead of the plain [`IC`](#direct-printing) functio. A
similar result would be obtained if using `IC_FA` and `IC_FV` in place of
[`IC_A`](#return-value-and-icecream-apply-macro) and [`IC_V`](#range-views-pipeline)
respectively.
When using the formatting function variants (`IC_F` and `IC_FA`), the same formatting
string will be applied by default to all the arguments. That could be a problem if we wish
to have arguments with distinct formatting, or if the arguments have multiple types with
non mutually valid syntaxes. Therefore, to set a distinct formatting string to a specific
argument we can wrap it with the `IC_` function. The code:
```C++
auto a = int{42};
auto b = int{20};
IC_F("#X", a, IC_("d", b));
```
will print:
ic| a: 0X2A, b: 20
The `IC_` function can be used within the plain `IC` (or `IC_A`) function too:
```C++
auto a = int{42};
auto b = int{20};
IC(IC_("#x", a), b);
```
will print:
ic| a: 0x2a, b: 20
The last argument in an `IC_` function call is the one that will be printed, all other
arguments that come before the last will be converted to a string using the
[`to_string`](https://en.cppreference.com/w/cpp/string/basic_string/to_string) function
and concatenated as the resulting formatting string.
```C++
auto a = float{1.234};
auto width = int{7};
IC(IC_("*<",width,".3", a));
```
Will have as result a formatting string `"*<7.3"`, and will print:
ic| a: 1.23***
Just for completeness in the examples, an usage of `IC_FA` and `IC_FV` would be:
```C++
IC_FA("#x", my_function, 10, 20);
auto rv0 = vws::iota(0) | IC_FV("[::2]:#x", "bar") | vws::take(5);
```
This will print:
ic| 10: 0xa, 20: 0x14
and when iterating on `rv0`:
ic| bar[0]: 0
ic| bar[2]: 0x2
ic| bar[4]: 0x4
To `IC_F` and `IC_FA`, the syntax specification of the formatting strings depends both on
the type `T` being printed, and in that type's [printing strategy](#printing-strategies)
used by IceCream.
To `IC_FV`, the formatting syntax if the same as the [Range format
string](#range-format-string).
### Character Encoding
Character encoding in C++ is messy.
The `char8_t`, `char16_t`, and `char32_t` strings are well defined. They are capable, and
do hold Unicode code units of 8, 16, and 32 bits respectively, and they are encoded in
UTF-8, UTF-16, and UTF-32 also respectively.
The `char` strings have a well defined code unit bit size (given by
[`CHAR_BIT`](https://en.cppreference.com/w/cpp/types/climits), usually 8 bits), but there
are no requirements about its encoding.
The `wchar_t` strings have [neither a well defined code unit
size](https://en.cppreference.com/w/cpp/language/types#Character_types), nor any
requirements about its encoding.
In a code like this:
```C++
auto const str = std::string{"foo"};
std::cout << str;
```
We will have three character encoding points of interest. In the first one, before
compiling, that code will be in a source file in an unspecified "source encoding". In the
second interest point, the compiled binary will have the "foo" string saved in an
unspecified "execution encoding". Finally on the third point, the "foo" byte stream
received by `std::cout` will be ultimately forwarded to the system, that expects the
stream being encoded in an also unspecified "output encoding".
From that three interest points of character encoding, both "execution encoding", and
"output encoding" have impact in the inner working of Icecream-cpp, and there is no way to
know for sure what is the used encoding in both of them. In face of this uncertainty, the
adopted strategy is offer a reasonable default transcoding function, that will try convert
the data to the right encoding, and allow the user to use its own implementation when
needed.
Except for wide and Unicode string types (discussed below), when printing any other type
we will have its serialized textual data in "execution encoding". That "execution
encoding" may or may not be the same as the "output encoding", this one being the encoding
expected by the configured [output](#output). Because of that, before we send that data to
the output, we must transcode it to make sure that we have it in "output encoding". To
that end, before delivering the text data to the [output](#output), we send it to the
configured [output_transcoder](#output_transcoder) function, that must ensure it is
encoded in the correct "output encoding".
When printing the wide and Unicode string types, we need to have one more transcoding
level, because it is possible that the text data is in a distinct character encoding from
the expected "execution encoding". Because of that, additional logic is applied to make
sure that the strings are in "execution encoding" before we send them to output. This is
further discussed in [wide strings](#wide-strings), and [unicode
strings](#unicode-strings) sections.
### Configuration
The Icecream-cpp configuration system works "layered by scope". At the basis level we have
the global `IC_CONFIG` object. That global instance is shared by the whole running
program, as would be expected of a global variable. It is created with all config options
at its default values, and any change is readily seen by the whole program.
At any point of the code we can create a new config layer at the current scope by
instantiating a new `IC_CONFIG` variable, calling the `IC_CONFIG_SCOPE()` macro. All the
config options of this new instance will be in an "unset" state by default, and any
request to an option value not yet set will be delegated to its parent. That request will
go up on the parent chain until the first one having that option set answers.
All config options are set by using accessor methods of the `IC_CONFIG` object, and they
can be chained:
```C++
IC_CONFIG
.prefix("ic: ")
.show_c_string(false)
.line_wrap_width(70);
```
`IC_CONFIG` is just a regular variable with a funny name to make a collision extremely
unlikely. When calling any `IC*(...)` macro, it will pick the `IC_CONFIG` instance at
scope by doing an [unqualified name
lookup](https://en.cppreference.com/w/cpp/language/unqualified_lookup), using the same
rules applied to any other regular variable.
To summarize all the above, in the code:
```C++
auto my_function() -> void
{
IC_CONFIG.line_wrap_width(20);
IC_CONFIG_SCOPE();
IC_CONFIG.context_delimiter("|");
IC_CONFIG.show_c_string(true);
{
IC_CONFIG_SCOPE();
IC_CONFIG.show_c_string(false);
// A
}
// B
}
```
At line `A`, the value of `IC_CONFIG`'s `line_wrap_width`, `context_delimiter`, and
`show_c_string` will be respectively: `20`, `"|"`, and `false`.
After the closing of the innermost scope block, at line `B`, the value of `IC_CONFIG`'s
`line_wrap_width`, `context_delimiter`, and `show_c_string` will be respectively: `20`,
`"|"`, and `true`.
The reading and writing operations on `IC_CONFIG` objects are thread safe.
> [!NOTE]
> Any modification in an `IC_CONFIG`, other than to the global instance, will be seen only
> within the current scope. As consequence, those modifications won't propagate to the
> scope of any called function.
#### enable/disable
Enable or disable the output of `IC(...)` macro, *enabled* default.
- get:
```C++
auto is_enabled() const -> bool;
```
- set:
```C++
auto enable() -> Config&;
auto disable() -> Config&;
```
The code:
```C++
IC(1);
IC_CONFIG.disable();
IC(2);
IC_CONFIG.enable();
IC(3);
```
will print:
```
ic| 1: 1
ic| 3: 3
```
#### output
Sets where the serialized textual data will be printed. By default that data will be
printed on the standard error output, the same as `std::cerr`.
- get:
```C++
auto output() const -> std::function;
```
- set:
```C++
template
auto output(T&& t) -> Config&;
```
Where the type `T` can be any of:
- A class inheriting from `std::ostream`.
- A class having a method `push_back(char)`.
- An output iterator that accepts the operation `*it = 'c'`
For instance, the code:
```C++
auto str = std::string{};
IC_CONFIG.output(str);
IC(1, 2);
```
Will print the output `"ic| 1: 1, 2: 2\n"` on the `str` string.
> [!WARNING]
> Icecream-cpp won't take ownership of the argument `t`, so care must be taken by the user
> to ensure that it is alive.
#### prefix
A function that generate the text that will be printed before each output.
- get:
```C++
auto prefix() const -> std::function;
```
- set:
```C++
template
auto prefix(Ts&& ...values) -> Config&;
```
Where the types `Ts` can be any of:
- A string,
- A callable `T() -> U`, where `U` has an overload of `operator<<(ostream&, U)`.
The printed prefix will be a concatenation of all those elements.
The code:
```C++
IC_CONFIG.prefix("icecream| ");
IC(1);
IC_CONFIG.prefix([]{return 42;}, "- ");
IC(2);
IC_CONFIG.prefix("thread ", std::this_thread::get_id, " | ");
IC(3);
```
will print:
```
icecream| 1: 1
42- 2: 2
thread 1 | 3: 3
```
#### show_c_string
Controls if a `char*` variable should be interpreted as a null-terminated C string
(`true`) or a pointer to a `char` (`false`). The default value is `true`.
- get:
```C++
auto show_c_string() const -> bool;
```
- set:
```C++
auto show_c_string(bool value) -> Config&;
```
The code:
```C++
char const* flavor = "mango";
IC_CONFIG.show_c_string(true);
IC(flavor);
IC_CONFIG.show_c_string(false);
IC(flavor);
```
will print:
```
ic| flavor: "mango";
ic| flavor: 0x55587b6f5410
```
#### wide_string_transcoder
Function that transcodes a `wchar_t` string, from a system defined encoding to a `char`
string in the system "execution encoding".
- get:
```C++
auto wide_string_transcoder() const -> std::function;
```
- set:
```C++
auto wide_string_transcoder(std::function transcoder) -> Config&;
auto wide_string_transcoder(std::function transcoder) -> Config&;
```
There is no guarantee that the input string will end on a null terminator (this is the
actual semantic of string_view), so the user must observe the input string size value.
The default implementation will check if the C locale is set to other value than "C" or
"POSIX". If yes, it will forward the input to the
[std::wcrtomb](https://en.cppreference.com/w/cpp/string/multibyte/wcrtomb) function.
Otherwise, it will assume that the input is Unicode encoded (UTF-16 or UTF-32, accordingly
to the byte size of `wchar_t`), and transcoded it to UTF-8.
#### unicode_transcoder
Function that transcodes a `char32_t` string, from a UTF-32 encoding to a `char` string in
the system "execution encoding".
- get:
```C++
auto unicode_transcoder() const -> std::function;
```
- set:
```C++
auto unicode_transcoder(std::function transcoder) -> Config&;
auto unicode_transcoder(std::function transcoder) -> Config&;
```
There is no guarantee that the input string will end on a null terminator (this is the
actual semantic of string_view), so the user must observe the input string size value.
The default implementation will check the C locale is set to other value than "C" or
"POSIX". If yes, it will forward the input to the
[std::c32rtomb](https://en.cppreference.com/w/cpp/string/multibyte/c32rtomb) function.
Otherwise, it will just transcoded it to UTF-8.
This function will be used to transcode all the `char8_t`, `char16_t`, and `char32_t`
strings. When transcoding `char8_t` and `char16_t` strings, they will be first converted
to a `char32_t` string, before being sent as input to this function.
#### output_transcoder
Function that transcodes a `char` string, from the system "execution encoding" to a `char`
string in the system "output encoding", as expected by the configured [output](#output).
- get:
```C++
auto output_transcoder() const -> std::function;
```
- set:
```C++
auto output_transcoder(std::function transcoder) -> Config&;
auto output_transcoder(std::function transcoder) -> Config&;
```
There is no guarantee that the input string will end on a null terminator (this is the
actual semantic of string_view), so the user must observe the input string size value.
The default implementation assumes that the "execution encoding" is the same as the
"output encoding", and will just return an unchanged input.
#### line_wrap_width
The maximum number of characters before the output be broken on multiple lines. Default
value of `70`.
- get:
```C++
auto line_wrap_width() const -> std::size_t;
```
- set:
```C++
auto line_wrap_width(std::size_t value) -> Config&;
```
#### include_context
If the context (source name, line number, and function name) should be printed even when
printing variables. Default value is `false`.
- get:
```C++
auto include_context() const -> bool;
```
- set:
```C++
auto include_context(bool value) -> Config&;
```
#### context_delimiter
The string separating the context text from the variables values. Default value is `"- "`.
- get:
```C++
auto context_delimiter() const -> std::string;
```
- set:
```C++
auto context_delimiter(std::string const& value) -> Config&;
```
### Printing strategies
In order to be printable, a type `T` must satisfy one of the strategies described in the
next sections. If it happens that multiple strategies are satisfied, the one with the
higher precedence will be chosen.
The strategy with the highest precedence is to use the [STL stream-based
I/O](https://en.cppreference.com/w/cpp/io). Consequently, when printing an object of type
`T`, if there exist an overloaded function `operator<<(ostream&, T)`, it will be used.
#### C strings
C strings are ambiguous. Should a `char* foo` variable be interpreted as a pointer to a
single `char` or as a null-terminated string? Likewise, is the `char bar[]` variable an
array of single characters or a null-terminated string? Is `char baz[3]` an array with
three single characters or is it a string of size two plus a `'\0'`?
Each one of those interpretations of `foo`, `bar`, and `baz` would be printed in a
distinct way. To the code:
```C++
char flavor[] = "pistachio";
IC(flavor);
```
all three outputs below are correct, each one having a distinct interpretation of what
should be the `flavor` variable.
```
ic| flavor: 0x55587b6f5410
ic| flavor: ['p', 'i', 's', 't', 'a', 'c', 'h', 'i', 'o', '\0']
ic| flavor: "pistachio"
```
The IceCream-Cpp policy is handle any bounded `char` array (i.e.: array with a known size)
as an array of single characters. So the code:
```C++
char flavor[] = "chocolate";
IC(flavor);
```
will print:
```
ic| flavor: ['c', 'h', 'o', 'c', 'o', 'l', 'a', 't', 'e', '\0']
```
unbounded `char[]` arrays (i.e.: array with an unknown size) will decay to `char*`
pointers, and will be printed either as a string or a pointer as configured by the
[show_c_string](#show_c_string) option.
#### Wide strings
Any realization of `wchar_t` strings, like `wchar_t*`, `std::wstring`, and `std::string_view`
Since the [output](#output) expects a `char` string, we must convert the text data to that
format, making sure that it is in "execution encoding". Icecream-cpp implements a default
transcoder function for doing that, but is possible to customize it by setting the
[wide_string_transcoder](#wide_string_transcoder) option.
#### Unicode strings
Any realization of `char8_t`, `char16_t`, and `char32_t` strings, like `char32_t*`,
`std::u8string`, and `std::u16string_view`
Since the [output](#output) expects a `char` string, we must convert the data to that
format, making sure that it is in "execution encoding". Icecream-cpp implements a default
transcoder function for doing that, but is possible to customize it by setting the
[unicode_transcoder](#unicode_transcoder) option.
#### Streamable types
A type `T` is *streamable* if an overloading function `operator<<(std::ostream&, T)`is
defined. This is the printing strategy with the highest priority, so if that overload
exists to a type `T`, it will be the used strategy.
##### Streamable format string
The [STL stream-based I/O](https://en.cppreference.com/w/cpp/io) hasn't the concept of a
*formatting string*, all the configurations are done using
[manipulators](https://en.cppreference.com/w/cpp/io/manip). Because of that, we have
created a custom formatting string syntax, strongly based on
[{fmt}](https://fmt.dev/11.0/syntax/#format-specification-mini-language) and [STL
Formatting](https://en.cppreference.com/w/cpp/utility/format/spec).
It has the following specification:
```
format_spec ::= [[fill]align][sign]["#"][width]["." precision][type]
fill ::=
align ::= "<" | ">" | "v"
sign ::= "+" | "-"
width ::= integer
precision ::= integer
type ::= "a" | "A" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "o" | "x" | "X"
integer ::= digit+
digit ::= "0"..."9"
```
###### [[fill]align]
The fill character can be any char. The presence of a fill character is signaled by the
character following it, which must be one of the alignment options. The meaning of the
alignment options is as follows:
| Symbol | Meaning |
|--------|--------------------------------------------------------------------------------------------------------------------------------------------------------|
| `'<'` | Left align within the available space. |
| `'>'` | Right align within the available space. This is the default. |
| `'v'` | Internally align the data, with the fill character being placed between the digits and either the base or sign. Applies to integer and floating-point. |
Note that unless a minimum field width is defined, the field width will always be the same
size as the data to fill it, so that the alignment option has no meaning in this case.
###### [sign]
The sign option is only valid for number types, and can be one of the following:
| Symbol | Meaning |
|--------|-------------------------------------------------------------------------|
| `'+'` | A sign will be used for both nonnegative as well as negative numbers. |
| `'-'` | A sign will be used only for negative numbers. This is the default. |
###### ["#"]
Causes the “alternate form” to be used for the conversion. The alternate form is defined
differently for different types. This option is only valid for integer and floating-point
types. For integers, when binary, octal, or hexadecimal output is used, this option adds
the prefix respective "0b" ("0B"), "0", or "0x" ("0X") to the output value. Whether the
prefix is lower-case or upper-case is determined by the case of the type specifier, for
example, the prefix "0x" is used for the type 'x' and "0X" is used for 'X'. For
floating-point numbers the alternate form causes the result of the conversion to always
contain a decimal-point character, even if no digits follow it. Normally, a decimal-point
character appears in the result of these conversions only if a digit follows it. In
addition, for 'g' and 'G' conversions, trailing zeros are not removed from the result.
###### [width]
A decimal integer defining the minimum field width. If not specified, then the field width
will be determined by the content.
###### ["." precision]
The precision is a decimal number indicating how many digits should be displayed after the
decimal point for a floating-point value formatted with 'f' and 'F', or before and after
the decimal point for a floating-point value formatted with 'g' or 'G'. For non-number
types the field indicates the maximum field size - in other words, how many characters
will be used from the field content. The precision is not allowed for integer, character,
Boolean, and pointer values. Note that a C string must be null-terminated even if
precision is specified.
###### [type]
Determines how the data should be presented.
The available integer presentation types are:
| Symbol | Meaning |
|--------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| `'d'` | Decimal integer. Outputs the number in base 10. |
| `'o'` | Octal format. Outputs the number in base 8. |
| `'x'` | Hex format. Outputs the number in base 16, using lower-case letters for the digits above 9. Using the '#' option with this type adds the prefix "0x" to the output value. |
| `'X'` | Hex format. Outputs the number in base 16, using upper-case letters for the digits above 9. Using the '#' option with this type adds the prefix "0X" to the output value. |
The available presentation types for floating-point values are:
| Symbol | Meaning |
|--------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| `'a'` | Hexadecimal floating point format. Prints the number in base 16 with prefix "0x" and lower-case letters for digits above 9. Uses 'p' to indicate the exponent. |
| `'A'` | Same as 'a' except it uses upper-case letters for the prefix, digits above 9 and to indicate the exponent. |
| `'e'` | Exponent notation. Prints the number in scientific notation using the letter ‘e’ to indicate the exponent. |
| `'E'` | Exponent notation. Same as 'e' except it uses an upper-case 'E' as the separator character. |
| `'f'` | Fixed point. Displays the number as a fixed-point number. |
| `'F'` | Fixed point. Same as 'f', but converts nan to NAN and inf to INF. |
| `'g'` | General format. For a given precision p >= 1, this rounds the number to p significant digits and then formats the result in either fixed-point format or in scientific notation, depending on its magnitude. A precision of 0 is treated as equivalent to a precision of 1. |
| `'G'` | General format. Same as 'g' except switches to 'E' if the number gets too large. The representations of infinity and NaN are uppercased, too. |
#### Pointer like types
The `std::unique_ptr` (before C++20) and `boost::scoped_ptr` types will be printed
like usual raw pointers.
The `std::weak_ptr` and `boost::weak_ptr` types will print their address if they are
valid or "expired" otherwise. The code:
```C++
auto v0 = std::make_shared(7);
auto v1 = std::weak_ptr {v0};
IC(v1);
v0.reset();
IC(v1);
```
will print:
```
ic| v1: 0x55bcbd840ec0
ic| v1: expired
```
#### Range types
A range is any type able to provide a [`begin`, `end`) iterator pair. In precise terms,
the Icecream-cpp library is able to print a range type `R` if it fulfills the
[`forward_range`](https://en.cppreference.com/w/cpp/ranges/forward_range) concept. In
roughly terms, a range type `R` having an iterator type `I` and a sentinel type `S` (used
to mark the end of the range, can be the same type as `I`) is a forward range if all the
following operations are valid:
```C++
I i0 = begin(r);
S s = end(r);
I i1(i0);
i0 == i1
i0 != i1
i0 == s
i0 != s
++i0;
*i0;
```
If all that operations are valid, the type `R` is not [streamable](#streamable-types) but
the elements inside `R` are, IceCream will print all items within `R` in place of `R`
itself.
The code:
```C++
auto v0 = std::list{10, 20, 30};
IC(v0);
```
will print:
ic| v0: [10, 20, 30]
Although lazily printing one item at a time, instead of the whole range at once. The
[`IC_V`](#range-views-pipeline) function is printing a range too.
##### Range format string
The accepted formatting string to a range type is a combination of both a range formatting
and its elements formatting. The range formatting is syntactically and semantically almost
identical to the [Python
slicing](https://docs.python.org/3/reference/expressions.html#slicings).
Formally, the accepted range types formatting string is:
```
format_spec ::= [range_fmt][":"elements_fmt]
range_fmt ::= "[" slicing | index "]"
slicing ::= [lower_bound] ":" [upper_bound] [ ":" [stride] ]
lower_bound ::= integer
upper_bound ::= integer
stride ::= integer
index ::= integer
integer ::= ["-"]digit+
digit ::= "0"..."9"
```
The same `elements_fmt` string will be used by all the printing elements, so it will have
the same syntax as the formatting string of the range elements.
The code:
```C++
auto arr = std::vector{10, 11, 12, 13, 14, 15};
IC_F("[:2:-1]:#x", arr);
```
will print:
ic| arr: [:2:-1]->[0xf, 0xe, 0xd]
Even though the specification says that `lower_bound`, `upper_bound`, `stride`, and
`index`, can have any integer value, some `range` capabilities can restrict them to just
positive values.
If a `range` is not [`sized`](https://en.cppreference.com/w/cpp/ranges/sized_range), the
`lower_bound`, `upper_bound`, and `index` values must be positive. Similarly, if a `range`
is not [`bidirectional`](https://en.cppreference.com/w/cpp/ranges/bidirectional_range) the
`stride` value must be positive too.
When printing within a [range views pipeline](#range-views-pipeline) using the `IC_FV`
function, all the `lower_bound`, `upper_bound`, and `index` values must be positive.
#### Tuple like types
A `std::pair` or `std::tuple` typed variables will print all of its
elements.
The code:
```C++
auto v0 = std::make_pair(10, 3.14);
auto v1 = std::make_tuple(7, 6.28, "bla");
IC(v0, v1);
```
will print:
```
ic| v0: (10, 3.14), v1: (7, 6.28, "bla")
```
##### Tuple like format string
The tuple like formatting specification is based on the syntax suggested in the
[Formatting
Ranges](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2286r8.html#pair-and-tuple-specifiers)
paper. Since that part hasn't done to the proposal, with any future change we may revisit
it here too.
```
tuple_spec ::= [casing][content]
casing ::= "n" | "m"
content ::= (delimiter element_fmt){N}
delimiter ::=
element_fmt ::=
```
Where the number `N` of repetitions in `content` rule is the tuple size.
The code:
```C++
auto v0 = std::make_tuple(20, "foo", 0.0123);
IC_F("n|#x||.3e", v0);
```
will print:
```
ic| ic| v0: 0x14, "foo", 1.230e-02
```
###### casing
Controls the tuple enclosing characters and separator. If not used, the default behavior
is to enclose the values between `"("` and `")"`, and separated by `", "`.
If `n` is used, the tuple won't be enclosed by parentheses. If `m` is used the tuple will
be printed "map value like", i.e.: not enclosed by parentheses and using `": "` as
separator. The `m` specifier is valid just to a *pair* or *2-tuple*.
###### content
The formatting string of each tuple element, separated by a `delimiter` character. This
can be any character, which value will be defined by the fist read `char` when parsing
this rule.
Each `element_fmt` string will be forwarded to the respective tuple element when printing
it, so it must follow the formatting specification of that particular element type.
#### Optional types
A `std::optional` typed variable will print its value, if it has one, or *nullopt*
otherwise.
The code:
```C++
auto v0 = std::optional {10};
auto v1 = std::optional {};
IC(v0, v1);
```
will print:
```
ic| v0: 10, v1: nullopt
```
#### Variant types
A `std::variant` or `boost::variant2::variant` typed variable will print its
value.
The code:
```C++
auto v0 = std::variant {4.2};
IC(v0);
```
will print:
```
ic| v0: 4.2
```
#### Exception types
Types inheriting from `std::exception` will print the return of `std::exception::what()`
method. If beyond that it inherits from `boost::exception` too, the response of
`boost::diagnostic_information()` will be also printed.
The code:
```C++
auto v0 = std::runtime_error("error description");
IC(v0);
```
will print:
```
ic| v0: error description
```
#### Not streamable types (Clang only)
If using Clang >= 15, a class will be printable even without an `operator<<(ostream&, T)` overload.
The code:
```C++
class S
{
public:
float f;
int ii[3];
};
S s = {3.14, {1,2,3}};
IC(s);
```
will print:
```
ic| s: {f: 3.14, ii: [1, 2, 3]}
```
## Pitfalls
`IC(...)` is a preprocessor macro, it can cause conflicts if there is some
other `IC` identifier on code. To change the `IC(...)` macro to a longer `ICECREAM(...)`
one, just define `ICECREAM_LONG_NAME` before the inclusion of `icecream.hpp` header:
```C++
#define ICECREAM_LONG_NAME
#include "icecream.hpp"
```
While most compilers will work just fine, until the C++20 the standard requires at least
one argument when calling a variadic macro. To handle this the nullary macros `IC0()` and
`ICECREAM0()` are defined alongside `IC(...)` and `ICECREAM(...)`.
[CI.badge]: https://github.com/renatoGarcia/icecream-cpp/workflows/CI/badge.svg
[CI.link]: https://github.com/renatoGarcia/icecream-cpp/actions?query=workflow%3ACI
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[LICENSE.link]: https://raw.githubusercontent.com/renatoGarcia/icecream-cpp/master/LICENSE.txt