Determines the size, in bytes, of the multibyte character whose first byte is pointed to by s.
If s is a null pointer, resets the global conversion state and(until C23) determined whether shift sequences are used.
This function is equivalent to the call mbtowc((wchar_t*)0, s, n), except that conversion state of mbtowc is unaffected.
[edit] Parameters s - pointer to the multibyte character n - limit on the number of bytes in s that can be examined [edit] Return valueIf s is not a null pointer, returns the number of bytes that are contained in the multibyte character or -1 if the first bytes pointed to by s do not form a valid multibyte character or â0â if s is pointing at the null charcter '\0'.
If s is a null pointer, resets its internal conversion state to represent the initial shift state and(until C23) returns â0â if the current multibyte encoding is not state-dependent (does not use shift sequences) or a non-zero value if the current multibyte encoding is state-dependent (uses shift sequences).
Each call to mblen updates the internal global conversion state (a static object of type mbstate_t, only known to this function). If the multibyte encoding uses shift states, care must be taken to avoid backtracking or multiple scans. In any case, multiple threads should not call mblen without synchronization: mbrlen may be used instead.
mblen is not allowed to have an internal state.
#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// the number of characters in a multibyte string is the sum of mblen()'s
// note: the simpler approach is mbstowcs(NULL, str, sz)
size_t strlen_mb(const char* ptr)
{
size_t result = 0;
const char* end = ptr + strlen(ptr);
mblen(NULL, 0); // reset the conversion state
while(ptr < end) {
int next = mblen(ptr, end - ptr);
if (next == -1) {
perror("strlen_mb");
break;
}
ptr += next;
++result;
}
return result;
}
void dump_bytes(const char* str)
{
for (const char* end = str + strlen(str); str != end; ++str)
printf("%02X ", (unsigned char)str[0]);
printf("\n");
}
int main(void)
{
setlocale(LC_ALL, "en_US.utf8");
const char* str = "z\u00df\u6c34\U0001f34c";
printf("The string \"%s\" consists of %zu characters, but %zu bytes: ",
str, strlen_mb(str), strlen(str));
dump_bytes(str);
}
Possible output:
The string "zÃæ°´ð" consists of 4 characters, but 10 bytes: 7A C3 9F E6 B0 B4 F0 9F 8D 8C[edit] References
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