πŸ’Ύ Archived View for gmi.noulin.net β€Ί man β€Ί man3 β€Ί strncpy.3.gmi captured on 2024-08-31 at 14:18:53. Gemini links have been rewritten to link to archived content

View Raw

More Information

⬅️ Previous capture (2023-09-08)

-=-=-=-=-=-=-

STRCPY(3)                                                               Linux Programmer's Manual                                                              STRCPY(3)

NAME
       strcpy, strncpy - copy a string

SYNOPSIS
       #include <string.h>

       char *strcpy(char *restrict dest, const char *src);
       char *strncpy(char *restrict dest, const char *restrict src, size_t n);

DESCRIPTION
       The  strcpy()  function  copies  the string pointed to by src, including the terminating null byte ('\0'), to the buffer pointed to by dest.  The strings may not
       overlap, and the destination string dest must be large enough to receive the copy.  Beware of buffer overruns!  (See BUGS.)

       The strncpy() function is similar, except that at most n bytes of src are copied.  Warning: If there is no null byte among the first n bytes of src,  the  string
       placed in dest will not be null-terminated.

       If the length of src is less than n, strncpy() writes additional null bytes to dest to ensure that a total of n bytes are written.

       A simple implementation of strncpy() might be:

           char *
           strncpy(char *dest, const char *src, size_t n)
           {
               size_t i;

               for (i = 0; i < n && src[i] != '\0'; i++)
                   dest[i] = src[i];
               for ( ; i < n; i++)
                   dest[i] = '\0';

               return dest;
           }

RETURN VALUE
       The strcpy() and strncpy() functions return a pointer to the destination string dest.

ATTRIBUTES
       For an explanation of the terms used in this section, see attributes(7).

       β”Œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”
       β”‚Interface                                                                                                                             β”‚ Attribute     β”‚ Value   β”‚
       β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€
       β”‚strcpy(), strncpy()                                                                                                                   β”‚ Thread safety β”‚ MT-Safe β”‚
       β””β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”˜

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

NOTES
       Some  programmers consider strncpy() to be inefficient and error prone.  If the programmer knows (i.e., includes code to test!)  that the size of dest is greater
       than the length of src, then strcpy() can be used.

       One valid (and intended) use of strncpy() is to copy a C string to a fixed-length buffer while ensuring both that the buffer is not overflowed  and  that  unused
       bytes  in  the  destination buffer are zeroed out (perhaps to prevent information leaks if the buffer is to be written to media or transmitted to another process
       via an interprocess communication technique).

       If there is no terminating null byte in the first n bytes of src, strncpy() produces an unterminated string in dest.  If buf has length  buflen,  you  can  force
       termination using something like the following:

           if (buflen > 0) {
               strncpy(buf, str, buflen - 1);
               buf[buflen - 1]= '\0';
           }

       (Of course, the above technique ignores the fact that, if src contains more than buflen - 1 bytes, information is lost in the copying to dest.)

   strlcpy()
       Some systems (the BSDs, Solaris, and others) provide the following function:

           size_t strlcpy(char *dest, const char *src, size_t size);

       This  function  is  similar  to strncpy(), but it copies at most size-1 bytes to dest, always adds a terminating null byte, and does not pad the destination with
       (further) null bytes.  This function fixes some of the problems of strcpy() and strncpy(), but the caller must still handle the possibility of data loss if  size
       is too small.  The return value of the function is the length of src, which allows truncation to be easily detected: if the return value is greater than or equal
       to size, truncation occurred.  If loss of data matters, the caller must either check the arguments before the call, or test the function return value.  strlcpy()
       is not present in glibc and is not standardized by POSIX, but is available on Linux via the libbsd library.

BUGS
       If the destination string of a strcpy() is not large enough, then anything might happen.  Overflowing fixed-length string buffers is a favorite cracker technique
       for taking complete control of the machine.  Any time a program reads or copies data into a buffer, the program first needs to check that there's  enough  space.
       This  may  be  unnecessary  if you can show that overflow is impossible, but be careful: programs can get changed over time, in ways that may make the impossible
       possible.

SEE ALSO
       bcopy(3), memccpy(3), memcpy(3), memmove(3), stpcpy(3), stpncpy(3), strdup(3), string(3), wcscpy(3), wcsncpy(3)

GNU                                                                            2021-03-22                                                                      STRCPY(3)