What is vswscanf_s() in C?

vswscanf_s() reads a formatted list of arguments from a buffer; the vswscanf_s() function validates the arguments at runtime before the read operation. The declaration for vswscanf_s() is shown below:

int vswscanf_s( wchar_t *buffer, const wchar_t *format, va_list args);

Note: The vswscan_s function is not supported by some compilers. If a compiler supports vswscanf_s, the value of STDC_WANT_LIB_EXT1 is set to 1.

Parameters

buffer: Pointer to the wide-character array from where the input is to be read.
format: Format in which the input will be read.
args: Pointer to the list of arguments in which data will be read.

Return value

If the read operation from the buffer is successful, vswscanf_s() returns the number of arguments that are read. If the read operation is not successful, EOFEnd-of-File is returned.

Example

Consider the code snippet below, which demonstrates the use of vswscanf_s():

#include <stdio.h>
#include <wchar.h>
#include <stdarg.h>
int readformatted (const wchar_t * buffer, const wchar_t * format, ...)
{
  int len=0;
  va_list arg_list;
  va_start (arg_list, format);
  len = vswscanf_s (buffer, format, arg_list);
  va_end (arg_list);
  return len;
}
int main ()
{
  wchar_t buffer[80] = L"This is vswscanf Example code";
  
  wchar_t buff[5][200];
  int len = readformatted(buffer, L" %s %s %s %s %s %s", buff[0] , buff[1] , buff[2] , buff[3] , buff[4] );
  printf("Buffer Content: %s %s %s %s %s \n", buff[0] , buff[1] , buff[2] , buff[3] , buff[4] );
  printf("Number of arguments read from file: %d \n", len);
  
   return 0;
}

Output

Buffer Content: This is vswscanf Example code 
Number of arguments read from file: 5

Explanation

The readformatted() function in line 21 uses vswscanf_s() in line 10 to read the content of the buffer. The content of the buffer is written to buff, which is created in line 19.

Note: The function above is not supported by the GCC compiler, hence you will get an implicit declaration of function vswscanf_s error. Use the following variant to get the job done: int vswscanf( wchar_t *buffer, const wchar_t *format, va_list args);.

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