mirror of
https://github.com/nlohmann/json.git
synced 2024-08-23 05:22:28 +02:00
88 lines
1.4 KiB
Markdown
88 lines
1.4 KiB
Markdown
|
# FAQ
|
||
|
|
||
|
## Parsing
|
||
|
|
||
|
### How can I parse from a string?
|
||
|
|
||
|
```cpp
|
||
|
json j = json::parse("[1,2,3,4]");
|
||
|
```
|
||
|
|
||
|
You can pass string literals (as above), `std::string`, `const char*` or byte containers such as `std::vector<uint8_t>`.
|
||
|
|
||
|
### How can I parse from a file?
|
||
|
|
||
|
```cpp
|
||
|
std::ifstream i("your_file.json");
|
||
|
json j = json::parse(i);
|
||
|
```
|
||
|
|
||
|
## Serialization
|
||
|
|
||
|
### How can I serialize a JSON value
|
||
|
|
||
|
```cpp
|
||
|
std::cout << j << std::endl;
|
||
|
```
|
||
|
|
||
|
This is equivalent to
|
||
|
|
||
|
```cpp
|
||
|
std::string s = j.dump();
|
||
|
std::cout << s << std::endl;
|
||
|
```
|
||
|
|
||
|
### How can I pretty-print a JSON value
|
||
|
|
||
|
```cpp
|
||
|
std::cout << std::setw(4) << j << std::endl;
|
||
|
```
|
||
|
|
||
|
This is equivalent to
|
||
|
|
||
|
```cpp
|
||
|
std::string s = j.dump(4);
|
||
|
std::cout << s << std::endl;
|
||
|
```
|
||
|
|
||
|
The number `4` denotes the number of spaces used for indentation.
|
||
|
|
||
|
## Iterating
|
||
|
|
||
|
### How can I iterate over a JSON value?
|
||
|
|
||
|
```cpp
|
||
|
for (json& val : j)
|
||
|
{
|
||
|
// val is a reference for the current value
|
||
|
}
|
||
|
```
|
||
|
|
||
|
This works with any JSON value, also primitive values like numbers.
|
||
|
|
||
|
### How can I access the keys when iterating over a JSON object?
|
||
|
|
||
|
```cpp
|
||
|
for (auto it = j.begin(); it != j.end(); ++it)
|
||
|
{
|
||
|
// the value
|
||
|
json &val = it.value();
|
||
|
|
||
|
// the key (for objects)
|
||
|
const std::string &key = it.key();
|
||
|
}
|
||
|
```
|
||
|
|
||
|
You can also use an iteration wrapper and use range for:
|
||
|
|
||
|
```cpp
|
||
|
for (auto it : json::iteration_wrapper(j))
|
||
|
{
|
||
|
// the value
|
||
|
json &val = it.value();
|
||
|
|
||
|
// the key (for objects)
|
||
|
const std::string &key = it.key();
|
||
|
}
|
||
|
```
|