1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
3 .\" %%%LICENSE_START(VERBATIM)
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13 .\" Since the Linux kernel and libraries are constantly changing, this
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21 .\" Formatted or processed versions of this manual, if unaccompanied by
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25 .\" References consulted:
26 .\" Linux libc source code
27 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
29 .\" Modified Sat Jul 24 18:11:47 1993 by Rik Faith (faith@cs.unc.edu)
30 .\" 2007-06-15, Marc Boyer <marc.boyer@enseeiht.fr> + mtk
31 .\" Improve discussion of strncat().
32 .TH STRCAT 3 2014-01-20 "GNU" "Linux Programmer's Manual"
34 strcat, strncat \- concatenate two strings
37 .B #include <string.h>
39 .BI "char *strcat(char *" dest ", const char *" src );
41 .BI "char *strncat(char *" dest ", const char *" src ", size_t " n );
51 overwriting the terminating null byte (\(aq\\0\(aq) at the end of
53 and then adds a terminating null byte.
54 The strings may not overlap, and the
57 enough space for the result.
60 is not large enough, program behavior is unpredictable;
61 .IR "buffer overruns are a favorite avenue for attacking secure programs" .
65 function is similar, except that
74 does not need to be null-terminated if it contains
80 the resulting string in
82 is always null-terminated.
97 plus the terminating null byte).
98 Therefore, the size of
101 .IR "strlen(dest)+n+1" .
103 A simple implementation of
110 strncat(char *dest, const char *src, size_t n)
112 size_t dest_len = strlen(dest);
115 for (i = 0 ; i < n && src[i] != \(aq\\0\(aq ; i++)
116 dest[dest_len + i] = src[i];
117 dest[dest_len + i] = \(aq\\0\(aq;
128 functions return a pointer to the resulting string
131 .SS Multithreading (see pthreads(7))
136 functions are thread-safe.
138 SVr4, 4.3BSD, C89, C99.
140 Some systems (the BSDs, Solaris, and others) provide the following function:
142 size_t strlcat(char *dest, const char *src, size_t size);
144 This function appends the null-terminated string
149 .IR "size\-strlen(dest)\-1"
152 and adds a null terminator to the result,
157 This function fixes the buffer overrun problem of
159 but the caller must still handle the possibility of data loss if
162 The function returns the length of the string
164 tried to create; if the return value is greater than or equal to
167 If data loss matters, the caller
169 either check the arguments before the call, or test the function return value.
171 is not present in glibc and is not standardized by POSIX,
172 .\" https://lwn.net/Articles/506530/
173 but is available on Linux via the