Programming

Code:

#include<iostream.h>
#include<string>
#include<stdio.h>

int main()
{
         char *cmd="delete backup backup-iso image a.iso b.iso c.iso d.iso";
         char *tokenized_cmd,*sub_cmd;

        sub_cmd=strstr(cmd,"image");
        tokenized_cmd=strtok(sub_cmd," ");

        while(tokenized_cmd != NULL)
        {
                tokenized_cmd=strtok(NULL," ");
                if(tokenized_cmd!=NULL)
                {
                        cout<<tokenized_cmd<<" ";
                }
        }

}

The output i expect here is :
a.iso b.iso c.iso d.iso
i.e.,whatever is there after the word "image".

but the command tokenized_cmd=strtok(cmd," ");
is throwing segmentation fault!!

Any mistakes you could find in the snippet??

strtok() needs to be able to modify the buffer it's scanning. As declared, you cannot modify cmd (which sub_cmd references). Use an array instead of a pointer declaration.

For more info: http://c-faq.com/decl/strlitinit.html

Regards,
Alister

Thanks Alister!
But i checked the strtok syntax shows: char * strtok ( char * str, const char * delimiters );

This was a sample program i was trying. In the original code, the cmd is actually passed to a function from elsewhere as const char* which i've done strdup to get char*.

So is there a way to do this by keeping cmd as char*?

any alternate way...

It's the memory that's important, not the labels. Unwritable remains unwritable memory even after you force a 'const char *' pointer into 'char *'. Which is what you are doing by putting "strings" into 'char *' variables, incidentally.

A "string" like that is a const char *, even though you're shoving it into a "char *" pointer. You've not done strdup() here, and are trying to modify the original "string" which resides in read-only memory.

Again, 'char *' is just a label. Putting a "string" inside a "char *" does not make it modifiable.

You'll just have to make a duplicate, either with strdup() or by saving into your own local buffer.

Code:

char buf[512];
strcpy(buf, "string");