mirror of
https://github.com/nlohmann/json.git
synced 2025-07-19 17:03:16 +03:00
85 lines
2.0 KiB
Markdown
85 lines
2.0 KiB
Markdown
# JSON_ASSERT
|
|
|
|
```cpp
|
|
#define JSON_ASSERT(x) /* value */
|
|
```
|
|
|
|
This macro controls which code is executed for [runtime assertions](../../features/assertions.md) of the library.
|
|
|
|
## Parameters
|
|
|
|
`x` (in)
|
|
: expression of scalar type
|
|
|
|
## Default definition
|
|
|
|
The default value is [`#!cpp assert(x)`](https://en.cppreference.com/w/cpp/error/assert).
|
|
|
|
```cpp
|
|
#define JSON_ASSERT(x) assert(x)
|
|
```
|
|
|
|
Therefore, assertions can be switched off by defining `NDEBUG`.
|
|
|
|
## Notes
|
|
|
|
- The library uses numerous assertions to guarantee invariants and to abort in case of otherwise undefined behavior
|
|
(e.g., when calling [operator[]](../basic_json/operator%5B%5D.md) with a missing object key on a `const` object). See
|
|
page [runtime assertions](../../features/assertions.md) for more information.
|
|
- Defining the macro to code that does not call `std::abort` may leave the library in an undefined state.
|
|
- The macro is undefined outside the library.
|
|
|
|
## Examples
|
|
|
|
??? example "Example 1: default behavior"
|
|
|
|
The following code will trigger an assertion at runtime:
|
|
|
|
```cpp
|
|
#include <nlohmann/json.hpp>
|
|
|
|
using json = nlohmann::json;
|
|
|
|
int main()
|
|
{
|
|
const json j = {{"key", "value"}};
|
|
auto v = j["missing"];
|
|
}
|
|
```
|
|
|
|
Output:
|
|
|
|
```
|
|
Assertion failed: (m_value.object->find(key) != m_value.object->end()), function operator[], file json.hpp, line 2144.
|
|
```
|
|
|
|
??? example "Example 2: user-defined behavior"
|
|
|
|
The assertion reporting can be changed by defining `JSON_ASSERT(x)` differently.
|
|
|
|
```cpp
|
|
#include <cstdio>
|
|
#include <cstdlib>
|
|
#define JSON_ASSERT(x) if(!(x)){fprintf(stderr, "assertion error in %s\n", __FUNCTION__); std::abort();}
|
|
|
|
#include <nlohmann/json.hpp>
|
|
|
|
using json = nlohmann::json;
|
|
|
|
int main()
|
|
{
|
|
const json j = {{"key", "value"}};
|
|
auto v = j["missing"];
|
|
}
|
|
```
|
|
|
|
Output:
|
|
|
|
```
|
|
assertion error in operator[]
|
|
```
|
|
|
|
## Version history
|
|
|
|
- Added in version 3.9.0.
|