vswprintf() function in C/C++
This vswprintf() function writes the wide string to the wide string buffer. A maximum of (len-1) wide characters are written to buffer which is followed by a null wide character.
Syntax:
int vswprintf( wchar_t* ws, size_t len, const wchar_t* format, va_list arg )
Parameters: The function accepts four mandatory parameters which are described below:
- ws: specifies the pointer to a given wide string buffer which will store the result
- len: specifies the maximum length of wide characters written back to the buffer including the terminating null character
- format: specifies the pointer to a null terminated wide string
- arg: specifies the value identifying a variable arguments list
Note: All format specifiers have the same meaning as in printf therefore, %lc shall be used to write a wide character ( and not %c ), as well as %ls shall be used for wide strings ( and not %s ).
Return value: The function returns two value as below:
- On success, the vswprintf() function returns number of wide characters written excluding the terminating null wide character.
- A negative number is returned on failure, including when the resulting string to be written to ws would be longer than n characters.
Below programs illustrate the above function:
Program 1 :
// C++ program to illustrate the // vswprintf() function #include <bits/stdc++.h> using namespace std; // function to check the number // of wide characters written void find ( wchar_t * ws, size_t len, const wchar_t *format, ... ) { // hold the variable argument va_list arg; // A function that invokes va_start // shall also invoke va_end before it returns. va_start ( arg, format ); vswprintf ( ws, len, format, arg ); va_end ( arg ); } // Driver code int main () { // buffer with size 60 wchar_t ws[60]; // initializing the string as latin characters wchar_t str[] = L "\u0025 \u0026 \u0027 \u0028 \u0029" ; // print the letters find(ws, 60, L "Some Latin letters : %ls\n" , str); wprintf(L " %ls " , ws); return 0; } |
Some Latin letters : % & ' ( )
Program 2 :
// C++ program to illustrate the // vswprintf() function // When the size of the buffer is smaller // than the total length of the string written #include <bits/stdc++.h> using namespace std; // function to check the number // of wide characters written void find ( wchar_t * ws, size_t len, const wchar_t *format, ... ) { // hold the variable argument va_list arg; // A function that invokes va_start // shall also invoke va_end before it returns. va_start ( arg, format ); vswprintf ( ws, len, format, arg ); va_end ( arg ); } // Driver code int main () { // initializing the string as english characters wchar_t str[] = L "Geek for Beginner" ; // buffer with size 20 wchar_t ws[20]; find(ws, 20, L "GFG is : %ls\n" , str); wprintf(L "%ls" , ws); return 0; } |
GFG is : Geek for g
Note: If the resulting string would be longer than n-1 wide characters, the remaining characters are discarded and not stored.