#include <stdlib.h> size_t mbstowcs(wchar_t *restrict pwcs, const char *restrict s, size_t n);
The mbstowcs() function converts a sequence of characters from the array pointed to by s into a sequence of corresponding wide-character codes and stores not more than n wide-character codes into the array pointed to by pwcs. No characters that follow a null byte (which is converted into a wide-character code with value 0) will be examined or converted. Each character is converted as if by a call to mbtowc(3C).
No more than n elements will be modified in the array pointed to by pwcs. If copying takes place between objects that overlap, the behavior is undefined.
The behavior of this function is affected by the LC_CTYPE category of the current locale. If pwcs is a null pointer, mbstowcs() returns the length required to convert the entire array regardless of the value of n, but no values are stored.
If an invalid character is encountered, mbstowcs() returns (size_t)−1 and may set errno to indicate the error. Otherwise, mbstowcs() returns the number of the array elements modified (or required if pwcs is NULL), not including a terminating 0 code, if any. The array will not be zero-terminated if the value returned is n.
The mbstowcs() function may fail if:
Invalid byte sequence is detected.
See attributes(5) for descriptions of the following attributes: