This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.
For loop without iterator_wrapper:
for (auto it = j_object.begin(); it != j_object.end(); ++it)
{
std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}
Range-based for loop without iterator proxy:
for (auto it : j_object)
{
std::cout << "value: " << it << '\n';
}
Range-based for loop with iterator proxy:
{
std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}
- Note
- When iterating over an array,
key()
will return the index of the element as string (see example).
- Parameters
-
[in] | ref | reference to a JSON value |
- Returns
- iteration proxy object wrapping ref with an interface to use in range-based for loops
- Example
- The following code shows how the wrapper is used
2 #include <nlohmann/json.hpp>
9 json j_object = {{
"one", 1}, {
"two", 2}};
10 json j_array = {1, 2, 4, 8, 16};
15 std::cout <<
"key: " << x.key() <<
", value: " << x.value() <<
'\n';
21 std::cout <<
"key: " << x.key() <<
", value: " << x.value() <<
'\n';
Output (play with this example online): key: one, value: 1
key: two, value: 2
key: 0, value: 1
key: 1, value: 2
key: 2, value: 4
key: 3, value: 8
key: 4, value: 16
The example code above can be translated withg++ -std=c++11 -Isingle_include doc/examples/iterator_wrapper.cpp -o iterator_wrapper
- Exception safety
- Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
- Complexity
- Constant.
- Note
- The name of this function is not yet final and may change in the future.
- Deprecated:
- This stream operator is deprecated and will be removed in future 4.0.0 of the library. Please use items() instead; that is, replace
json::iterator_wrapper(j)
with j.items()
.
Definition at line 19001 of file json.hpp.