объединить две строки (concatenate two strings)
Имя (Name)
strcat, strncat - concatenate two strings
Синопсис (Synopsis)
#include <string.h>
char *strcat(char *restrict dest, const char *restrict src);
char *strncat(char *restrict dest, const char *restrict src, size_t n);
Описание (Description)
The strcat() function appends the src string to the dest string,
overwriting the terminating null byte ('\0') at the end of dest,
and then adds a terminating null byte. The strings may not
overlap, and the dest string must have enough space for the
result. If dest is not large enough, program behavior is
unpredictable; buffer overruns are a favorite avenue for
attacking secure programs.
The strncat() function is similar, except that
* it will use at most n bytes from src; and
* src does not need to be null-terminated if it contains n or
more bytes.
As with strcat(), the resulting string in dest is always null-
terminated.
If src contains n or more bytes, strncat() writes n+1 bytes to
dest (n from src plus the terminating null byte). Therefore, the
size of dest must be at least strlen(dest)+n+1.
A simple implementation of strncat() might be:
char *
strncat(char *dest, const char *src, size_t n)
{
size_t dest_len = strlen(dest);
size_t i;
for (i = 0 ; i < n && src[i] != '\0' ; i++)
dest[dest_len + i] = src[i];
dest[dest_len + i] = '\0';
return dest;
}
Возвращаемое значение (Return value)
The strcat() and strncat() functions return a pointer to the
resulting string dest.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│strcat(), strncat() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
Примечание (Note)
Some systems (the BSDs, Solaris, and others) provide the
following function:
size_t strlcat(char *dest, const char *src, size_t size);
This function appends the null-terminated string src to the
string dest, copying at most size-strlen(dest)-1 from src, and
adds a terminating null byte to the result, unless size is less
than strlen(dest). This function fixes the buffer overrun
problem of strcat(), but the caller must still handle the
possibility of data loss if size is too small. The function
returns the length of the string strlcat() tried to create; if
the return value is greater than or equal to size, data loss
occurred. If data loss matters, the caller must either check the
arguments before the call, or test the function return value.
strlcat() is not present in glibc and is not standardized by
POSIX, but is available on Linux via the libbsd library.
Примеры (Examples)
Because strcat() and strncat() must find the null byte that
terminates the string dest using a search that starts at the
beginning of the string, the execution time of these functions
scales according to the length of the string dest. This can be
demonstrated by running the program below. (If the goal is to
concatenate many strings to one target, then manually copying the
bytes from each source string while maintaining a pointer to the
end of the target string will provide better performance.)
Program source
#include <stdint.h>
#include <string.h>
#include <time.h>
#include <stdio.h>
int
main(int argc, char *argv[])
{
#define LIM 4000000
char p[LIM + 1]; /* +1 for terminating null byte */
time_t base;
base = time(NULL);
p[0] = '\0';
for (int j = 0; j < LIM; j++) {
if ((j % 10000) == 0)
printf("%d %jd\n", j, (intmax_t) (time(NULL) - base));
strcat(p, "a");
}
}
Смотри также (See also)
bcopy(3), memccpy(3), memcpy(3), strcpy(3), string(3),
strncpy(3), wcscat(3), wcsncat(3)
