#include <string.h> char *stpncpy(char dst[restrict .sz], const char *restrict src, size_t sz); char *strncpy(char dst[restrict .sz], const char *restrict src, size_t sz);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
stpncpy():
Since glibc 2.10: _POSIX_C_SOURCE >= 200809L Before glibc 2.10: _GNU_SOURCE
An implementation of these functions might be:
char *
stpncpy(char *restrict dst, const char *restrict src, size_t sz)
{
bzero(dst, sz);
return mempcpy(dst, src, strnlen(src, sz));
}
char *
strncpy(char *restrict dst, const char *restrict src, size_t sz)
{
stpncpy(dst, src, sz);
return dst;
}
Interface | Attribute | Value |
stpncpy(), strncpy() | Thread safety | MT-Safe |
It's impossible to distinguish truncation by the result of the call, from a character sequence that just fits the destination buffer; truncation should be detected by comparing the length of the input string with the size of the destination buffer.
If you're going to use this function in chained calls, it would be useful to develop a similar function that accepts a pointer to the end (one after the last element) of the destination buffer instead of its size.
int
main(void)
{
char *p;
char buf1[20];
char buf2[20];
size_t len;
if (sizeof(buf1) < strlen("Hello world!"))
warnx("stpncpy: truncating character sequence");
p = stpncpy(buf1, "Hello world!", sizeof(buf1));
len = p - buf1;
printf("[len = %zu]: ", len);
printf("%.*s\n", (int) len, buf1); // "Hello world!"
if (sizeof(buf2) < strlen("Hello world!"))
warnx("strncpy: truncating character sequence");
strncpy(buf2, "Hello world!", sizeof(buf2));
len = strnlen(buf2, sizeof(buf2));
printf("[len = %zu]: ", len);
printf("%.*s\n", (int) len, buf2); // "Hello world!"