[c] string help

saiz66 · 10-05-2004, 07:28 PM

Hi. I wanted to know if it was possible to cut the first part of a string from a substring that I wanted to search. for ex.

string1 = "Here is a sample file."
string2 = "a"

if i wanted to find an occurence of a in string1 i would type:

printf("%s\n", strstr (string1, string2));

this would output "a sample file."

But how would I output the first part? "Here is"

Thanks.

crabboy · 10-05-2004, 11:01 PM

#include <stdio.h>

main()
{
char a[] = "Here is a sample file";
char b[] = "a";
char * c = NULL;

printf("%s\n", strstr( a, b ));

c = strstr(a, b );
*c = '\0';
printf( "%s\n", a );

}

CroMagnon · 10-05-2004, 11:04 PM

Code:

    char *string1 = "Here is a sample file.";
    char *string2 = "a";
    char *sub;

    sub = strstr( string1, string2 );
    if (sub) {
        printf( "%s\n", strndup( string1, sub - string1 ) );  // !!!
    }

Note that strndup() allocates memory for you, so you would be better to save the return pointer and free() it later. If your program is short and doesn't use much memory you can get by without it, but I think you would run into problems if you tried to scale up (memory leaks), so it's better to do it correctly from the start...

saiz66 · 10-05-2004, 11:45 PM

thanks a lot!

Also, does anybody know if strcpy() would copy over a char * c? or do both arguments have to be char c[100]? And if that is the case how can I get around this? I dont want to have a fixed size. thanks.

CroMagnon · 10-06-2004, 01:00 AM

Yes, but the buffer pointed to by c has to be large enough to contain the data - if you have a 50 character string and you try to strcpy it into a 40 character buffer, you're either going to cause a crash or start writing over memory that you shouldn't, with god-knows-what consequences. Also, unless you check the sizes of your buffers beforehand, you really shouldn't use strcpy over strncpy.