concat const char * with char * Post: 302288963

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Top Forums Programming concat const char * with char * Post 302288963 by ujeshm on Wednesday 18th of February 2009 12:01:36 PM

02-18-2009

Registered User

"const char *foo means it cannot be modified" -> This is not completly correct. 'const char *foo' means foo is a pointer which points to a constant char (pointer to a constant variable, not a constant pointer variable). That means, the address in foo can be changed(foo is not a constant), but we cannot modify the value contained in the address held by foo(the value is considered as constant).

For example

Code:

const char *foo;

foo="Test1";

cout<<"\n foo 1 : "<<foo<<endl;  // Result will be 'Test1'

foo="Foo is changed now."       

cout<<"\n foo 2 : "<<foo<<endl;  // Result will be 'Foo is changed now'

In your code,

you got error in line 6 because, you are trying to change the value contained in the address held by 'dest'. That is if you remove the '*' it wont generate any errors. But the meaning will be different.

you got error in 7 because the dest is a const char * variable. memcpy does not allow const char * as its first argument (memcpy(void *,const void *,size_t))

The work around you are suggesting is similar to what I have given in my previous post. Only difference is you are asking to assign the address of the const char * variable to a char * variable and change the content of the char * variable. I declared the char * variable first and assigned its address to the const char * variable. After that I am also doing the same thing.

I think my previous post created some miss understandings in you. Sorry if it is so.

Last edited by ujeshm; 02-18-2009 at 02:15 PM..

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LEARN ABOUT FREEBSD

string

STRING(3)						   BSD Library Functions Manual 						 STRING(3)

NAME

     stpcpy, strcat, strncat, strchr, strrchr, strcmp, strncmp, strcasecmp, strncasecmp, strcpy, strncpy, strerror, strlen, strpbrk, strsep,
     strspn, strcspn, strstr, strtok, index, rindex -- string specific functions

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <string.h>

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

     char *
     strcat(char *s, const char * append);

     char *
     strncat(char *s, const char *append, size_t count);

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

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

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

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

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

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

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

     char *
     strncpy(char *dst, const char *src, size_t count);

     char *
     strerror(int errno);

     size_t
     strlen(const char *s);

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

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

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

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

     char *
     strstr(const char *big, const char *little);

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

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

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

DESCRIPTION

     The string functions manipulate strings terminated by a null byte.

     See the specific manual pages for more information.  For manipulating variable length generic objects as byte strings (without the null byte
     check), see bstring(3).

     Except as noted in their specific manual pages, the string functions do not test the destination for size limitations.

SEE ALSO

     bstring(3), index(3), rindex(3), stpcpy(3), strcasecmp(3), strcat(3), strchr(3), strcmp(3), strcpy(3), strcspn(3), strerror(3), strlen(3),
     strpbrk(3), strrchr(3), strsep(3), strspn(3), strstr(3), strtok(3)

STANDARDS

     The strcat(), strncat(), strchr(), strrchr(), strcmp(), strncmp(), strcpy(), strncpy(), strerror(), strlen(), strpbrk(), strspn(), strcspn(),
     strstr(), and strtok() functions conform to ISO/IEC 9899:1990 (``ISO C90'').

BSD
								 December 11, 1993							       BSD

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