#define JSON_USE_GLOBAL_UDLS /* value */
When defined to 1, the user-defined string literals (UDLs) are placed into the global namespace instead of nlohmann::literals::json_literals.
The default value is 1.
#define JSON_USE_GLOBAL_UDLS 1
When the macro is not defined, the library will define it to its default value.
!!! info “Future behavior change”
The user-defined string literals will be removed from the global namespace in the next major release of the library. To prepare existing code, define `JSON_USE_GLOBAL_UDLS` to `0` and bring the string literals into scope where needed. Refer to any of the [string literals](#see-also) for details.
!!! hint “CMake option”
The placement of user-defined string literals can also be controlled with the CMake option [`JSON_GlobalUDLs`](../../integration/cmake.md#json_globaludls) (`ON` by default) which defines `JSON_USE_GLOBAL_UDLS` accordingly.
??? example “Example 1: Default behavior”
The code below shows the default behavior using the `_json` UDL.
```cpp
#include <nlohmann/json.hpp>
#include <iostream>
int main()
{
auto j = "42"_json;
std::cout << j << std::endl;
}
```
Output:
```json
42
```
??? example “Example 2: Namespaced UDLs”
The code below shows how UDLs need to be brought into scope before using `_json` when `JSON_USE_GLOBAL_UDLS` is
defined to `0`.
```cpp
#define JSON_USE_GLOBAL_UDLS 0
#include <nlohmann/json.hpp>
#include <iostream>
int main()
{
// auto j = "42"_json; // This line would fail to compile,
// because the UDLs are not in the global namespace
// Bring the UDLs into scope
using namespace nlohmann::json_literals;
auto j = "42"_json;
std::cout << j << std::endl;
}
```
Output:
```json
42
```