concat const char * with char * Post: 302288503

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Top Forums Programming concat const char * with char * Post 302288503 by jim mcnamara on Tuesday 17th of February 2009 12:03:39 PM

02-17-2009

Registered User

I get this with a C99-compliant compiler:

Code:

csaprd:/home/jmcnama> cc t.c
cc: "t.c", line 6: error 1549: Modifiable lvalue required for assignment operator.
cc: "t.c", line 7: warning 611: Type conversion loses "const" qualifier.
cc: "t.c", line 7: warning 563: Argument #1 is not the correct type.

on this code:

Code:

#include <string.h>
#include <stdlib.h>

const char *mystrcpy(const char *dest,const char *source, const size_t len)
{
    *dest=0x0;
	memcpy(dest, source, len);
	return dest;
}

int main()
{
    char dest[10]={0x0};    
    const char *p=mystrcpy(dest, "test", 4);
    printf("%s\n", dest);
    return 0;
}

const char *foo means it cannot be modified (the "modifiable lvalue" complaint), for example. ujeshm may use a non-standard compiler or a really old one that allows it.

You can work around it by copying a const char into a regular string then modifying the new string.

Note: A warning means the code did not compile correctly, and if it runs you are then coding by coincidence and will sooner or later cause serious problems that are difficult to resolve.

If you are using gcc, compile

Code:

gcc -Wall mycode.c

to see full errors and warnings.

jim mcnamara

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string

STRING(3)						     Linux Programmer's Manual							 STRING(3)

NAME

       stpcpy, strcasecmp, strcat, strchr, strcmp, strcoll, strcpy, strcspn, strdup, strfry, strlen, strncat, strncmp, strncpy, strncasecmp, strp-
       brk, strrchr, strsep, strspn, strstr, strtok, strxfrm, index, rindex - string operations

SYNOPSIS

       #include <strings.h>

       int strcasecmp(const char *s1, const char *s2);

       int strncasecmp(const char *s1, const char *s2, size_t n);

       char *index(const char *s, int c);

       char *rindex(const char *s, int c);

       #include <string.h>

       char *stpcpy(char *dest, const char *src);

       char *strcat(char *dest, const char *src);

       char *strchr(const char *s, int c);

       int strcmp(const char *s1, const char *s2);

       int strcoll(const char *s1, const char *s2);

       char *strcpy(char *dest, const char *src);

       size_t strcspn(const char *s, const char *reject);

       char *strdup(const char *s);

       char *strfry(char *string);

       size_t strlen(const char *s);

       char *strncat(char *dest, const char *src, size_t n);

       int strncmp(const char *s1, const char *s2, size_t n);

       char *strncpy(char *dest, const char *src, size_t n);

       char *strpbrk(const char *s, const char *accept);

       char *strrchr(const char *s, int c);

       char *strsep(char **stringp, const char *delim);

       size_t strspn(const char *s, const char *accept);

       char *strstr(const char *haystack, const char *needle);

       char *strtok(char *s, const char *delim);

       size_t strxfrm(char *dest, const char *src, size_t n);

DESCRIPTION

       The string functions perform string operations on null-terminated strings.  See the individual man pages for descriptions of each function.

SEE ALSO

       index(3), rindex(3), stpcpy(3), strcasecmp(3), strcat(3), strchr(3), strcmp(3), strcoll(3), strcpy(3),  strcspn(3),  strdup(3),	strfry(3),
       strlen(3),  strncasecmp(3),  strncat(3),  strncmp(3),  strncpy(3),  strpbrk(3),	strrchr(3),  strsep(3),  strspn(3),  strstr(3), strtok(3),
       strxfrm(3)

COLOPHON

       This page is part of release 3.44 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

								    2010-02-25								 STRING(3)

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