1STRCPY(3)                  Linux Programmer's Manual                 STRCPY(3)
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NAME

6       strcpy, strncpy - copy a string
7

SYNOPSIS

9       #include <string.h>
10
11       char *strcpy(char *dest, const char *src);
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13       char *strncpy(char *dest, const char *src, size_t n);
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DESCRIPTION

16       The  strcpy()  function  copies the string pointed to by src, including
17       the terminating null byte ('\0'), to the buffer  pointed  to  by  dest.
18       The  strings  may  not overlap, and the destination string dest must be
19       large enough to receive the copy.  Beware  of  buffer  overruns!   (See
20       BUGS.)
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22       The  strncpy()  function is similar, except that at most n bytes of src
23       are copied.  Warning: If there is no null byte among the first n  bytes
24       of src, the string placed in dest will not be null-terminated.
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26       If  the  length of src is less than n, strncpy() writes additional null
27       bytes to dest to ensure that a total of n bytes are written.
28
29       A simple implementation of strncpy() might be:
30
31           char *
32           strncpy(char *dest, const char *src, size_t n)
33           {
34               size_t i;
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36               for (i = 0; i < n && src[i] != '\0'; i++)
37                   dest[i] = src[i];
38               for ( ; i < n; i++)
39                   dest[i] = '\0';
40
41               return dest;
42           }
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RETURN VALUE

45       The strcpy() and strncpy() functions return a pointer to  the  destina‐
46       tion string dest.
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ATTRIBUTES

49       For   an   explanation   of   the  terms  used  in  this  section,  see
50       attributes(7).
51
52       ┌────────────────────┬───────────────┬─────────┐
53       │Interface           │ Attribute     │ Value   │
54       ├────────────────────┼───────────────┼─────────┤
55       │strcpy(), strncpy() │ Thread safety │ MT-Safe │
56       └────────────────────┴───────────────┴─────────┘

CONFORMING TO

58       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
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NOTES

61       Some programmers consider strncpy() to be inefficient and error  prone.
62       If  the  programmer knows (i.e., includes code to test!)  that the size
63       of dest is greater than the length of src, then strcpy() can be used.
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65       One valid (and intended) use of strncpy() is to copy a C  string  to  a
66       fixed-length  buffer  while  ensuring both that the buffer is not over‐
67       flowed and that unused bytes in the destination buffer are  zeroed  out
68       (perhaps to prevent information leaks if the buffer is to be written to
69       media or transmitted to another process via an interprocess  communica‐
70       tion technique).
71
72       If  there  is  no  terminating  null  byte in the first n bytes of src,
73       strncpy() produces an unterminated string in dest.  If buf  has  length
74       buflen, you can force termination using something like the following:
75
76           if (buflen &