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https://github.com/vivkin/gason
Lightweight and fast JSON parser for C++
https://github.com/vivkin/gason
Last synced: about 2 months ago
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Lightweight and fast JSON parser for C++
- Host: GitHub
- URL: https://github.com/vivkin/gason
- Owner: vivkin
- License: mit
- Created: 2013-10-28T08:27:09.000Z (almost 11 years ago)
- Default Branch: master
- Last Pushed: 2022-08-24T08:15:22.000Z (about 2 years ago)
- Last Synced: 2024-06-20T13:30:10.141Z (3 months ago)
- Language: C++
- Homepage:
- Size: 129 KB
- Stars: 336
- Watchers: 26
- Forks: 49
- Open Issues: 12
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# gason
gason is new version of [vjson](https://code.google.com/p/vjson) parser. It's still very **fast** and have very **simple interface**. Completly new api, different internal representation and using new C++ standard features explains why parser get a new name.
- [Features](#features)
- [Installation](#installation)
- [Usage](#usage)
- [Parsing](#parsing)
- [Iteration](#iteration)
- [Notes](#notes)
- [NaN-boxing](#nan-boxing)
- [Memory management](#memory-management)
- [Parser internals](#parser-internals)
- [Performance](#performance)
- [License](#license)
## Features
* No dependencies
* Small codebase (~450 loc)
* Small memory footprint (16-24B per value)
gason is **not strict** parser:
* Source buffer can contain more than one value (first will be parsed; pointer to the rest returns)
* Single number, string or identifier will be succesfully parsed
* Trailing `,` before closing `]` or `}` is not an error
gason is **destructive** parser, i.e. your **source buffer** will be **modified**! Strings stored as pointers to source buffer, where closing `"` (or any other symbol, if string have escape sequences) replaced with `'\0'`. Arrays and objects are represented as single linked list (without random access).
## Installation
1. Download latest [gason.h](https://raw.github.com/vivkin/gason/master/src/gason.h) and [gason.cpp](https://raw.github.com/vivkin/gason/master/src/gason.cpp)
2. Compile with C++11 support (`-std=c++11` flag for gcc/clang)
3. ...
4. PROFIT!
## Usage
### Parsing
```cpp
#include "gason.h"
...
char *source = get_useless_facebook_response(); // or read file, whatever
// do not forget terminate source string with 0
char *endptr;
JsonValue value;
JsonAllocator allocator;
int status = jsonParse(source, &endptr, &value, allocator);
if (status != JSON_OK) {
fprintf(stderr, "%s at %zd\n", jsonStrError(status), endptr - source);
exit(EXIT_FAILURE);
}
```
All **values** will become **invalid** when **allocator** be **destroyed**. For print verbose error message see `printError` function in [pretty-print.cpp](pretty-print.cpp).
### Iteration
```cpp
double sum_and_print(JsonValue o) {
double sum = 0;
switch (o.getTag()) {
case JSON_NUMBER:
printf("%g\n", o.toNumber());
sum += o.toNumber();
break;
case JSON_STRING:
printf("\"%s\"\n", o.toString());
break;
case JSON_ARRAY:
for (auto i : o) {
sum += sum_and_print(i->value);
}
break;
case JSON_OBJECT:
for (auto i : o) {
printf("%s = ", i->key);
sum += sum_and_print(i->value);
}
break;
case JSON_TRUE:
fprintf(stdout, "true");
break;
case JSON_FALSE:
fprintf(stdout, "false");
break;
case JSON_NULL:
printf("null\n");
break;
}
return sum;
}
...
double sum = sum_and_print(value);
printf("sum of all numbers: %g\n", sum);
```
Arrays and Objects use the same `JsonNode` struct, but for arrays valid only `next` and `value` fields!
## Notes
### NaN-boxing
gason stores values using NaN-boxing technique. By [IEEE-754](http://en.wikipedia.org/wiki/IEEE_floating_point) standard we have 2^52-1 variants for encoding double's [NaN](http://en.wikipedia.org/wiki/NaN). So let's use this to store value type and payload:
```
sign
| exponent
| |
[0][11111111111][yyyyxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx]
| |
tag |
payload
```
48 bits payload [enough](http://en.wikipedia.org/wiki/X86-64#Virtual_address_space_details) for store any pointer on x64. Numbers use zero tag, so infinity and nan are accessible.
### Memory management
JsonAllocator allocates big blocks of memory and use pointer bumping inside theese blocks for smaller allocations. Size of block can be tuned by *JSON_ZONE_SIZE* constant (default 4 KiB).
### Parser internals
> [05.11.13, 2:52:33] Олег Литвин: о нихуя там свитч кейс на стеройдах!
Internally in `jsonParse` function nested arrays/objects stored in array of circulary linked list of `JsonNode`. Size of that array can be tuned by *JSON_STACK_SIZE* constant (default 32).
## Performance
For build parser shootout:
1. `clone-enemy-parser.sh` (need mercurial, git, curl, nodejs)
2. `cmake -DCMAKE_BUILD_TYPE=Release -DSHOOTOUT=ON`
Test files downloads from random repos on github:
* `big.json` - just big with big count escape sequences
* `monster.json` - 3d model, lot of numbers
* `data.json` - many objects
First column - parse time in microseconds, second - traverse and sum all numbers.
Intel Core i7 2.3 GHz, OSX 10.9, clang-500.2.79:
```
shootout/big.json: length 6072200
gason 20092us 71us (5520251617769.000000)
vjson 19723us 156us (5520251617769.000000)
sajson 25226us 128us (5520251617769.000000)
rapidjson 18093us 96us (5520251617769.000000)
shootout/data.json: length 17333
gason 75us 4us (3754.333493)
vjson 80us 5us (3754.333471)
sajson 117us 8us (3754.333493)
rapidjson 91us 7us (3754.333493)
shootout/monster.json: length 196473
gason 924us 162us (34474757.667613)
vjson 2218us 396us (34474757.667621)
sajson 1898us 380us (34474757.667613)
rapidjson 2210us 446us (34474757.667613)
```
Samsung Galaxy Note II (GT-N7100), Android 4.3, gcc 4.8.2:
```
I/ruberoid( 8944): /sdcard/Download/shootout/big.json: length 6072200
I/ruberoid( 8944): gason 66269us 561us (5520251617769.000000)
I/ruberoid( 8944): vjson 59052us 1058us (5520251617769.000000)
I/ruberoid( 8944): sajson 75240us 1573us (5520251617769.000000)
I/ruberoid( 8944): rapidjson 82948us 808us (5520251617769.000000)
I/ruberoid( 8944): /sdcard/Download/shootout/data.json: length 17333
I/ruberoid( 8944): gason 328us 32us (3754.333493)
I/ruberoid( 8944): vjson 316us 54us (3754.333471)
I/ruberoid( 8944): sajson 291us 55us (3754.333493)
I/ruberoid( 8944): rapidjson 386us 48us (3754.333493)
I/ruberoid( 8944): /sdcard/Download/shootout/monster.json: length 196473
I/ruberoid( 8944): gason 6330us 1342us (34474757.667613)
I/ruberoid( 8944): vjson 9481us 2236us (34474757.667621)
I/ruberoid( 8944): sajson 6400us 1971us (34474757.667613)
I/ruberoid( 8944): rapidjson 7464us 1745us (34474757.667613)
```
## License
Distributed under the MIT license. Copyright (c) 2013-2015, Ivan Vashchaev