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STRCPY(3)                  Linux Programmer's ManualSTRCPY(3)NAME       strcpy, strncpy - copy a stringSYNOPSIS       #include <string.h>       char *strcpy(char *dest, const char *src);       char *strncpy(char *dest, const char *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  destina-       tion string dest.ATTRIBUTES       For  an  explanation  of  the  terms  used  in  this  section,  see at-tributes(7).       +--------------------+---------------+---------+       |Interface           | Attribute     | Value   |       +--------------------+---------------+---------+       |strcpy(), strncpy() | Thread safety | MT-Safe |       +--------------------+---------------+---------+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 over-       flowed 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  communica-       tion 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 han-       dle 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  any-       thing  might  happen.  Overflowing fixed-length string buffers is a fa-       vorite 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  unneces-       sary  if you can show that overflow is impossible, but be careful: pro-       grams can get changed over time, in ways that may make  the  impossible       possible.SEE ALSObcopy(3),memccpy(3),memcpy(3),memmove(3),stpcpy(3),stpncpy(3),strdup(3),string(3),wcscpy(3),wcsncpy(3)COLOPHON       This page is part of release 5.10 of the Linux  man-pages  project.   A       description  of  the project, information about reporting bugs, and the       latest    version    of    this    page,    can     be     found     at       https://www.kernel.org/doc/man-pages/.GNU                               2019-03-06STRCPY(3)