From cppreference.com
int vscanf( const char* format, std::va_list vlist );
(1) (since C++11) int vfscanf( std::FILE* stream, const char* format, std::va_list vlist ); (2) (since C++11)int vsscanf( const char* buffer, const char* format, std::va_list vlist );
(3) (since C++11)Reads data from a variety of sources, interprets it according to format and stores the results into locations defined by vlist.
1)Reads the data from
stdin.
2) Reads the data from file stream stream.
3) Reads the data from null-terminated character string buffer.
[edit] 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 vlist - variable argument list containing the receiving arguments.
The format string consists of
The following format specifiers are available:
Conversionhh h none l ll j z t L Only available since C++11â Yes Yes Yes Yes Yes %
Matches literal %.
c
Matches a character or a sequence of characters.
char*
wchar_t*
N/A N/A N/A N/A N/As
Matches a sequence of non-whitespace characters (a string).
[set ]
Matches a non-empty sequence of character from set of characters.
^, then all characters not in the set are matched.] or ^] then the ] character is also included into the set.- in the non-initial position in the scanset may be indicating a range, as in [0-9].d
Matches a decimal integer.
signed char* or unsigned char*
signed short* or unsigned short*
signed int* or unsigned int*
signed long* or unsigned long*
signed long long* or unsigned long long*
std::intmax_t*or
std::uintmax_t* std::size_t* std::ptrdiff_t* N/Ai
Matches an integer.
u
Matches an unsigned decimal integer.
o
Matches an unsigned octal integer.
x
X
Matches an unsigned hexadecimal integer.
n
Returns the number of characters read so far.
a (C++11)
A (C++11)
e
E
f
F (C++11)
g
G
Matches a floating-point number.
float*
double*
N/A N/A N/A N/Along double*
p
Matches implementation defined character sequence defining a pointer.
printf family of functions should produce the same sequence using %p format specifier.void**
N/A N/A N/A N/A N/A N/A NotesFor every conversion specifier other than n, the longest sequence of input characters which does not exceed any specified ï¬eld 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 ï¬rst 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-ï¬le, 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 std::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 std::mbrtowc with an std::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 (std::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 âsinkâ 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.
If a conversion specification is invalid, the behavior is undefined.
[edit] Return valueNumber of arguments successfully read, or EOF if failure occurs.
[edit] NotesAll 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.
#include <cstdarg>
#include <cstdio>
#include <iostream>
#include <stdexcept>
void checked_sscanf(int count, const char* buf, const char *fmt, ...)
{
std::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[edit] See also
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