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