basic_json::accept¶
// (1)
template<typename InputType>
static bool accept(InputType&& i,
const bool ignore_comments = false);
// (2)
template<typename IteratorType>
static bool accept(IteratorType first, IteratorType last,
const bool ignore_comments = false);
Checks whether the input is valid JSON.
- Reads from a compatible input.
-
Reads from a pair of character iterators
The value_type of the iterator must be a integral type with size of 1, 2 or 4 bytes, which will be interpreted respectively as UTF-8, UTF-16 and UTF-32.
Unlike the parse
function, this function neither throws an exception in case of invalid JSON input (i.e., a parse error) nor creates diagnostic information.
Template parameters¶
InputType
-
A compatible input, for instance:
- an
std::istream
object - a
FILE
pointer - a C-style array of characters
- a pointer to a null-terminated string of single byte characters
- an object
obj
for whichbegin(obj)
andend(obj)
produces a valid pair of iterators.
- an
IteratorType
- a compatible iterator type
Parameters¶
i
(in)- Input to parse from.
ignore_comments
(in)- whether comments should be ignored and treated like whitespace (
true
) or yield a parse error (false
); (optional,false
by default) first
(in)- iterator to start of character range
last
(in)- iterator to end of character range
Return value¶
Whether the input is valid JSON.
Exception safety¶
Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
Complexity¶
Linear in the length of the input. The parser is a predictive LL(1) parser.
Notes¶
(1) A UTF-8 byte order mark is silently ignored.
Examples¶
Example
The example below demonstrates the accept()
function reading from a string.
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// a valid JSON text
auto valid_text = R"(
{
"numbers": [1, 2, 3]
}
)";
// an invalid JSON text
auto invalid_text = R"(
{
"strings": ["extra", "comma", ]
}
)";
std::cout << std::boolalpha
<< json::accept(valid_text) << ' '
<< json::accept(invalid_text) << '\n';
}
Output:
true false
Version history¶
- Added in version 3.0.0.
- Ignoring comments via
ignore_comments
added in version 3.9.0.