operator<<(basic_json)¶
std::ostream& operator<<(std::ostream& o, const basic_json& j);
Serialize the given JSON value j to the output stream o. The JSON value will be serialized using the dump member function.
- The indentation of the output can be controlled with the member variable
widthof the output streamo. For instance, using the manipulatorstd::setw(4)onosets the indentation level to4and the serialization result is the same as callingdump(4). - The indentation character can be controlled with the member variable
fillof the output streamo. For instance, the manipulatorstd::setfill('\\t')sets indentation to use a tab character rather than the default space character.
Parameters¶
o(in, out)- stream to serialize to
j(in)- JSON value to serialize
Return value¶
the stream o
Exceptions¶
Throws type_error.316 if a string stored inside the JSON value is not UTF-8 encoded. Note that unlike the dump member functions, no error_handler can be set.
Complexity¶
Linear.
Examples¶
Example
The example below shows the serialization with different parameters to width to adjust the indentation level.
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// create JSON values
json j_object = {{"one", 1}, {"two", 2}};
json j_array = {1, 2, 4, 8, 16};
// serialize without indentation
std::cout << j_object << "\n\n";
std::cout << j_array << "\n\n";
// serialize with indentation
std::cout << std::setw(4) << j_object << "\n\n";
std::cout << std::setw(2) << j_array << "\n\n";
std::cout << std::setw(1) << std::setfill('\t') << j_object << "\n\n";
}
Output:
{"one":1,"two":2}
[1,2,4,8,16]
{
"one": 1,
"two": 2
}
[
1,
2,
4,
8,
16
]
{
"one": 1,
"two": 2
}
Version history¶
- Added in version 1.0.0
- Support for indentation character added in version 3.0.0.
Deprecation
This function replaces function std::ostream& operator>>(const basic_json& j, std::ostream& o) which has been deprecated in version 3.0.0. It will be removed in version 4.0.0. Please replace calls like j >> o; with o << j;.