Name

strcpy, strncpy
- copy a string

Library

libc.lib

Synopsis

  #include <string.h>
  char * stpcpy (char *dst, const char *src);
  char * strcpy (char * restrict dst, const char * restrict src);
  char * strncpy (char * restrict dst, const char * restrict src, size_t len);

Return values

The strcpy and strncpy functions return dst. The stpcpy function returns a pointer to the terminating ‘\0’ character of dst.

Detailed description

The stpcpy and strcpy functions copy the string src to dst (including the terminating ‘\0’ character.)

The strncpy function copies at most len characters from src into dst. If src is less than len characters long, the remainder of dst is filled with ‘\0’ characters. Otherwise, dst is not terminated.

Examples

#include <string.h>
#include <stdio.h>
int main()
{
    char one[50] = {"abcdefgh"};        
    printf("String before strcpy %s\n",one);
    strcpy(one,"Hello");
    printf("String after strcpy %s\n",one);
    strncpy(one + 5, " ",1);
    strncpy(one + 6, "World",5);
    printf("String after strncpy %s\n",one);
    return 0;   
}

Output 

String before strcpy abcdefgh
String after strcpy Hello
String after strncpy Hello World

Examples

The following sets chararray to "abc\0\0\0:" 
char chararray[6];
(void)strncpy(chararray, "abc", sizeof(chararray));

The following sets chararray to "abcdef:" 

char chararray[6];
(void)strncpy(chararray, "abcdefgh", sizeof(chararray));

Note that it does not NULL terminate chararray because the length of the source string is greater than or equal to the length argument.

The following copies as many characters from input to buf as will fit and NULL terminates the result. Because strncpy does not guarantee to NULL terminate the string itself, this must be done explicitly. 

char buf[1024];
(void)strncpy(buf, input, sizeof(buf) - 1);
buf[sizeof(buf) - 1] = ’\0’;

Security considerations

The strcpy function is easily misused in a manner which enables malicious users to arbitrarily change a running program’s functionality through a buffer overflow attack.

See also

bcopy, memcpy, memmove

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