std::vscanf, std::vfscanf, std::vsscanf
| Defined in header <cstdio>
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| int vscanf( const char* format, va_list vlist ); |
(1) | (since C++11) |
| int vfscanf( std::FILE* stream, const char* format, va_list vlist ); |
(2) | (since C++11) |
| int vsscanf( const char* buffer, const char* format, va_list vlist ); |
(3) | (since C++11) |
Reads data from the a variety of sources, interprets it according to format and stores the results into locations defined by vlist.
stream.buffer.Contents |
Parameters
| stream | - | input file stream to read from | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| buffer | - | pointer to a null-terminated character string to read from | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| format | - | pointer to a null-terminated character string specifying how to read the input.
The format string consists of
The following format specifiers are available:
For every conversion specifier other than n, the longest sequence of input characters which does not exceed any specified field width and which either is exactly what the conversion specifier expects or is a prefix of a sequence it would expect, is what's consumed from the stream. The first character, if any, after this consumed sequence remains unread. If the consumed sequence has length zero or if the consumed sequence cannot be converted as specified above, the matching failure occurs unless end-of-file, an encoding error, or a read error prevented input from the stream, in which case it is an input failure. All conversion specifiers other than [, c, and n consume and discard all leading whitespace characters (determined as if by calling isspace) before attempting to parse the input. These consumed characters do not count towards the specified maximum field width. The conversion specifiers lc, ls, and l[ perform multibyte-to-wide character conversion as if by calling mbrtowc with an mbstate_t object initialized to zero before the first character is converted. The conversion specifiers s and [ always store the null terminator in addition to the matched characters. The size of the destination array must be at least one greater than the specified field width. The use of %s or %[, without specifying the destination array size, is as unsafe as std::gets. The correct conversion specifications for the fixed-width integer types (int8_t, etc) are defined in the header <cinttypes> (although SCNdMAX, SCNuMAX, etc is synonymous with %jd, %ju, etc). There is a sequence point after the action of each conversion specifier; this permits storing multiple fields in the same "sink" variable. When parsing an incomplete floating-point value that ends in the exponent with no digits, such as parsing "100er" with the conversion specifier %f, the sequence "100e" (the longest prefix of a possibly valid floating-point number) is consumed, resulting in a matching error (the consumed sequence cannot be converted to a floating-point number), with "r" remaining. Some existing implementations do not follow this rule and roll back to consume only "100", leaving "er", e.g. glibc bug 1765.
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| vlist | - | variable argument list containing the receiving arguments | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Return value
Number of arguments successfully read, or EOF if failure occurs.
Notes
All these functions invoke va_arg at least once, the value of arg is indeterminate after the return. These functions to not invoke va_end, and it must be done by the caller.
Example
#include <iostream> #include <cstdio> #include <cstdarg> #include <stdexcept> void checked_sscanf(int count, const char* buf, const char *fmt, ...) { va_list ap; va_start(ap, fmt); if(std::vsscanf(buf, fmt, ap) != count) throw std::runtime_error("parsing error"); va_end(ap); } int main() { try { int n, m; std::cout << "Parsing '1 2'..."; checked_sscanf(2, "1 2", "%d %d", &n, &m); std::cout << "success\n"; std::cout << "Parsing '1 a'..."; checked_sscanf(2, "1 a", "%d %d", &n, &m); std::cout << "success\n"; } catch(const std::exception& e) { std::cout << e.what() << '\n'; } }
Output:
Parsing '1 2'...success Parsing '1 a'...parsing error
See also
| reads formatted input from stdin, a file stream or a buffer (function) | |
| prints formatted output to stdout, a file stream or a buffer using variable argument list (function) | |
| C documentation for vscanf, vfscanf, vsscanf
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