What is _snwprintf_s in C?

The _snwprintf_s function

The _snwprintf_s function is defined in the wchar.h standard library and is used to write formatted data to a string. The structure of the _snwprintf_s function is as follows:

int _snwprintf_s(wchat_t * buffer, size_t sizeOfBuffer, size_t count, const wchar_t * format, ...);

Parameters

  • buffer is a pointer to a wide character array to copy to.
  • sizeOfBuffer is the size of the buffer in words.
  • count is the maximum number of characters to copy.
  • format is a pointer to a wide character format string.
  • ... represents optional parameters passed due to the format string.

Return value

  • A positive number representing the number of characters copied to the buffer successfully.
  • A negative number if an error occurs.

Example usage of the _snwprintf_s function

The following code demonstrates the usage of the _snwprintf_s function:

#include<stdio.h>
#include<wchar.h>
int main() {
wchar_t buffer[100];
int i = 10, j = 8;
wchar_t format[] = L"You scored %d/%d";
int written = _snwprintf_s(buffer, 100, 15, format, j, i);
wprintf(L"Characters Written: %d\n", written);
wprintf(L"%S", buffer);
return 0;
}

Output:

Characters Written: 15
You scored 8/10

In the example above, the format string is copied to the buffer after the formatting is applied. The format string You scored %d/%d evaluates to You scored 8/10, because, in line 9, the argument right next to format is j and then i, which have the values 8 and 10 respectively. The function _snwprintf_s also returns the number of characters written to the buffer in the variable written. At the end of the program, the number of characters written and the contents of the buffer are printed onto the standard output.

Note: The function above is not supported by the GCC compiler, so you will get an implicit declaration of function… error.

Use the following variant _snwprintf to get the job done:

int _snwprintf(wchat_t * buffer, size_t count, const wchar_t * format, ...);

All parameters are the same as _snwprintf_s, except that sizeOfBuffer is not a parameter of _snwprintf. The return value of the above function is the same as _snwprintf_s.

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