| Functions | ||||||||||||||||||||||||||||||||||||
| Character manipulation | ||||||||||||||||||||||||||||||||||||
| Conversions to and from numeric formats | ||||||||||||||||||||||||||||||||||||
|
| |||||||||||||||||||||||||||||||||||
| String manipulation | ||||||||||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||||
| String examination | ||||||||||||||||||||||||||||||||||||
| Memory manipulation | ||||||||||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||||
| Miscellaneous | ||||||||||||||||||||||||||||||||||||
(C11)(C11) | ||||||||||||||||||||||||||||||||||||
Defined in header <string.h> | ||
| (1) | ||
char*strncat(char*dest,constchar*src,size_t count); | (until C99) | |
char*strncat(char*restrict dest,constchar*restrict src,size_t count); | (since C99) | |
errno_t strncat_s(char*restrict dest, rsize_t destsz, constchar*restrict src, rsize_t count); | (2) | (since C11) |
count characters from the character array pointed to bysrc, stopping if the null character is found, to the end of the null-terminated byte string pointed to bydest. The charactersrc[0] replaces the null terminator at the end ofdest. The terminating null character is always appended in the end (so the maximum number of bytes the function may write iscount+1).dest and the firstcount characters ofsrc, plus the terminating null character. The behavior is undefined if the source and destination objects overlap. The behavior is undefined if eitherdest is not a pointer to a null-terminated byte string orsrc is not a pointer to a character array,destsz) and that the following errors are detected at runtime and call the currently installedconstraint handler function:src ordest is a null pointerdestsz orcount is zero or greater thanRSIZE_MAXdestsz bytes ofdestcount or the length ofsrc, whichever is less, exceeds the space available between the null terminator ofdest anddestsz.dest <strnlen(dest,destsz)+strnlen(src,count)+1 <destsz; in other words, an erroneous value ofdestsz does not expose the impending buffer overflow. The behavior is undefined if the size of the character array pointed to bysrc <strnlen(src,count) <destsz; in other words, an erroneous value ofcount does not expose the impending buffer overflow.strncat_s is only guaranteed to be available if__STDC_LIB_EXT1__ is defined by the implementation and if the user defines__STDC_WANT_LIB_EXT1__ to the integer constant1 before including<string.h>.Contents |
| dest | - | pointer to the null-terminated byte string to append to |
| src | - | pointer to the character array to copy from |
| count | - | maximum number of characters to copy |
| destsz | - | the size of the destination buffer |
destdest is a null pointer ordestsz is zero or greater thanRSIZE_MAX).Becausestrncat needs to seek to the end ofdest on each call, it is inefficient to concatenate many strings into one usingstrncat.
Although truncation to fit the destination buffer is a security risk and therefore a runtime constraints violation forstrncat_s, it is possible to get the truncating behavior by specifyingcount equal to the size of the destination array minus one: it will copy the firstcount bytes and append the null terminator as always:strncat_s(dst,sizeof dst, src,(sizeof dst)-strnlen_s(dst,sizeof dst)-1);
#define __STDC_WANT_LIB_EXT1__ 1#include <string.h>#include <stdio.h>#include <stdlib.h> int main(void){char str[50]="Hello ";char str2[50]="World!";strcat(str, str2); strncat(str," Goodbye World!",3);puts(str); #ifdef __STDC_LIB_EXT1__ set_constraint_handler_s(ignore_handler_s);char s1[100]="good";char s5[1000]="bye";int r1= strncat_s(s1,100, s5,1000);// r1 is 0, s1 holds "goodbye\0"printf("s1 = %s, r1 = %d\n", s1, r1);char s2[6]="hello";int r2= strncat_s(s2,6,"",1);// r2 is 0, s2 holds "hello\0"printf("s2 = %s, r2 = %d\n", s2, r2);char s3[6]="hello";int r3= strncat_s(s3,6,"X",2);// r3 is non-zero, s3 holds "\0"printf("s3 = %s, r3 = %d\n", s3, r3);// the strncat_s truncation idiom:char s4[7]="abc";int r4= strncat_s(s4,7,"defghijklmn",3);// r4 is 0, s4 holds "abcdef\0"printf("s4 = %s, r4 = %d\n", s4, r4);#endif}
Possible output:
Hello World! Gos1 = goodbye, r1 = 0s2 = hello, r2 = 0s3 = , r3 = 22s4 = abcdef, r4 = 0
(C11) | concatenates two strings (function)[edit] |
(C11) | copies one string to another (function)[edit] |
(C23) | copies one buffer to another, stopping after the specified delimiter (function)[edit] |
C++ documentation forstrncat | |
