From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/c/string%2Fbyte%2Fstrcat.html | 76 +++++++++++++++++++++++++++++++++++ 1 file changed, 76 insertions(+) create mode 100644 devdocs/c/string%2Fbyte%2Fstrcat.html (limited to 'devdocs/c/string%2Fbyte%2Fstrcat.html') diff --git a/devdocs/c/string%2Fbyte%2Fstrcat.html b/devdocs/c/string%2Fbyte%2Fstrcat.html new file mode 100644 index 00000000..08ce3a04 --- /dev/null +++ b/devdocs/c/string%2Fbyte%2Fstrcat.html @@ -0,0 +1,76 @@ +

strcat, strcat_s

Defined in header <string.h>
(1) 
char *strcat( char *dest, const char *src );
+		 (until C99) 
char *strcat( char *restrict dest, const char *restrict src );
+		 (since C99) 
errno_t strcat_s(char *restrict dest, rsize_t destsz, const char *restrict src);
+		 (2) (since C11)
+1) Appends a copy of the null-terminated byte string pointed to by src to the end of the null-terminated byte string pointed to by dest. The character src[0] replaces the null terminator at the end of dest. The resulting byte string is null-terminated.
+ The behavior is undefined if the destination array is not large enough for the contents of both src and dest and the terminating null character. The behavior is undefined if the strings overlap. The behavior is undefined if either dest or src is not a pointer to a null-terminated byte string.
+2) Same as (1), except that it may clobber the rest of the destination array (from the last character written to destsz) with unspecified values and that the following errors are detected at runtime and call the currently installed constraint handler function: +
+ The behavior is undefined if the size of the character array pointed to by dest < strlen(dest)+strlen(src)+1 <= destsz; in other words, an erroneous value of destsz does not expose the impending buffer overflow. As with all bounds-checked functions, strcat_s only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <string.h>.

Parameters

+ + + +
dest - pointer to the null-terminated byte string to append to
src - pointer to the null-terminated byte string to copy from
destsz - maximum number of characters to write, typically the size of the destination buffer

Return value

+1) returns a copy of dest +
+2) returns zero on success, returns non-zero on error. Also, on error, writes zero to dest[0] (unless dest is a null pointer or destsz is zero or greater than RSIZE_MAX).

Notes

Because strcat needs to seek to the end of dest on each call, it is inefficient to concatenate many strings into one using strcat.

+

strcat_s is allowed to clobber the destination array from the last character written up to destsz in order to improve efficiency: it may copy in multibyte blocks and then check for null bytes.

+

The function strcat_s is similar to the BSD function strlcat, except that

+

Although strcat_s prohibits truncation due to potential security risks, it's possible to truncate a string using bounds-checked strncat_s instead.

+

Example

#define __STDC_WANT_LIB_EXT1__ 1
+#include <string.h> 
+#include <stdio.h>
+#include <stdlib.h>
+ 
+int main(void) 
+{
+    char str[50] = "Hello ";
+    char str2[50] = "World!";
+    strcat(str, str2);
+    strcat(str, " ...");
+    strcat(str, " Goodbye World!");
+    puts(str);
+ 
+#ifdef __STDC_LIB_EXT1__
+    set_constraint_handler_s(ignore_handler_s);
+    int r = strcat_s(str, sizeof str, " ... ");
+    printf("str = \"%s\", r = %d\n", str, r);
+    r = strcat_s(str, sizeof str, " and this is too much");
+    printf("str = \"%s\", r = %d\n", str, r);
+#endif
+}

Possible output:

+
Hello World! ... Goodbye World!
+str = "Hello World! ... Goodbye World! ... ", r = 0
+str = "", r = 22

References

See also

+ + + +
+
(C11)
 concatenates a certain amount of characters of two strings
(function)
+
(C11)
 copies one string to another
(function)
+
(C23)
 copies one buffer to another, stopping after the specified delimiter
(function)
C++ documentation for strcat
+

+ © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
+ https://en.cppreference.com/w/c/string/byte/strcat +

+
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