C Standard Library

C <stdlib.h> - mblen() Function

The C <stdlib.h> mblen() function returns the size (in bytes) of the multibyte character whose first byte is pointed to by str and examining at most n bytes.

This function has its own internal shift state, which is altered as necessary only by calling it. If str is a null pointer, it resets its internal conversion state to represent the initial shift state and returns whether multibyte encoding is state-dependent.


int mblen(const char *str, size_t n)


str Specify pointer to the multibyte character.
n Specify maximum number of bytes in str that can be examined.
size_t is an unsigned integral type.

Return Value

When str is not a null pointer, it returns the number of bytes that are contained in the multibyte character or -1 if the first bytes pointed to by str do not form a valid multibyte character or 0 if str is pointing at the null charcter '\0'.

When str is a null pointer, it returns 0 if the current multibyte encoding is not state-dependent or a non-zero value if the current multibyte encoding is state-dependent.


In the example below, mblen() and mbtowc() functions are used in the user-defined function printbuffer(), which prints a multibyte string character by character.

#include <stdio.h>
#include <stdlib.h>
void printbuffer (char* str, size_t n){
  int length;
  wchar_t dest;

  mblen (NULL, 0);         //reset mblen
  mbtowc (NULL, NULL, 0);  //reset mbtowc

  while (n > 0) {
    length = mblen(str, n);
    if (length < 1) 
    mbtowc(&dest, str, length);
    printf("[%lc]", dest);
    str = str + length; 
    n = n - length;

int main (){
  char str [] = "Hello World!";
  printbuffer (str, sizeof(str));
  return 0;

The output of the above code will be:

[H][e][l][l][o][ ][W][o][r][l][d][!]

❮ C <stdlib.h> Library