man3/strcat.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  22 .\"
  23 .\" References consulted:
  24 .\"     Linux libc source code
  25 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  26 .\"     386BSD man pages
  27 .\" Modified Sat Jul 24 18:11:47 1993 by Rik Faith (faith@cs.unc.edu)
  28 .\" 2007-06-15, Marc Boyer <marc.boyer@enseeiht.fr> + mtk
  29 .\"     Improve discussion of strncat().
  30 .TH STRCAT 3  2007-06-15 "GNU" "Linux Programmer's Manual"
  31 .SH NAME
  32 strcat, strncat \- concatenate two strings
  33 .SH SYNOPSIS
  34 .nf
  35 .B #include <string.h>
  36 .sp
  37 .BI "char *strcat(char *" dest ", const char *" src );
  38 .sp
  39 .BI "char *strncat(char *" dest ", const char *" src ", size_t " n );
  40 .fi
  41 .SH DESCRIPTION
  42 The
  43 .BR strcat ()
  44 function appends the \fIsrc\fP string to the
  45 \fIdest\fP string, overwriting the null byte (\(aq\\0\(aq) at the end of
  46 \fIdest\fP, and then adds a terminating null byte.
  47 The strings may not overlap, and the \fIdest\fP string must have
  48 enough space for the result.
  49 .PP
  50 The
  51 .BR strncat ()
  52 function is similar, except that
  53 .IP * 3
  54 it will use at most \fIn\fP characters from \fIsrc\fP; and
  55 .IP *
  56 \fIsrc\fP does not need to be null terminated if it contains
  57 \fIn\fP or more characters.
  58 .PP
  59 As with
  60 .BR strcat (),
  61 the resulting string in \fIdest\fP is always null terminated.
  62 .PP
  63 If \fIsrc\fP contains \fIn\fP or more characters,
  64 .BR strcat ()
  65 writes \fIn+1\fP characters to \fIdest\fP (\fIn\fP
  66 from \fIsrc\fP plus the terminating null byte).
  67 Therefore, the size of \fIdest\fP must be at least
  68 \fIstrlen(dest)+n+1\fP.
  69
  70 A simple implementation of
  71 .BR strncat ()
  72 might be:
  73 .in +4n
  74 .nf
  75
  76 char*
  77 strncat(char *dest, const char *src, size_t n)
  78 {
  79     size_t dest_len = strlen(dest);
  80     size_t i;
  81
  82     for (i = 0 ; i < n && src[i] != \(aq\\0\(aq ; i++)
  83         dest[dest_len + i] = src[i];
  84     dest[dest_len + i] = \(aq\\0\(aq;
  85
  86     return dest;
  87 }
  88 .fi
  89 .in
  90 .SH "RETURN VALUE"
  91 The
  92 .BR strcat ()
  93 and
  94 .BR strncat ()
  95 functions return a pointer to the resulting string \fIdest\fP.
  96 .SH "CONFORMING TO"
  97 SVr4, 4.3BSD, C89, C99.
  98 .SH "SEE ALSO"
  99 .BR bcopy (3),
 100 .BR memccpy (3),
 101 .BR memcpy (3),
 102 .BR strcpy (3),
 103 .BR strncpy (3),
 104 .BR wcscat (3),
 105 .BR wcsncat (3)