Networking Nslookup Utility using C.

[thriller500]

I had to make a wrapper program on "nslookup" networking utility and I am facing the following "Segmentation Fault error"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char* argv[])
{
		const char *d;
		char *s=NULL;
		char *x=NULL;
		d=argv[1];
		s="nslookup";
		x=strcat(s,d);	
		system(s);
		return 0;
}

I have no compilation errors.

Strcat function call:

char *strcat(char *s1, const char *s2);

I need some help because i am not able to figure out what i am doing wrong.

[Elkvis]

in order, as I can see it:

1. your variable names are non-descriptive, and therefore bad. name your variables what they really are. all but one is unnecessary anyway.
2. you're assigning to a pointer to const data after its declaration. while syntactically correct, it's far from good practice. it makes no sense for 'd' to be const in this case.
3. you're appending to a string that has only enough space reserved for its initial content. this is definitely the cause of your segmentation faults.
4. you don't need to store the return value of strcat. it appends to the buffer pointed to by the first parameter, and the return value is just a copy of that pointer. you're not using that return value anyway, so why store it?

[oogabooga]

You want to do something like this:

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

int main(int argc, char* argv[]) {

	char cmd[100] = "nslookup ";

	if (argc < 2) {
		fprintf(stderr, ":(\n");
		return 1;
	}

        strcat(cmd, argv[1]);  
        system(cmd);

        return 0;
}

[thriller500]

You want to do something like this:

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

int main(int argc, char* argv[]) {

    char cmd[100] = "nslookup ";

    if (argc < 2) {
        fprintf(stderr, ":(\n");
        return 1;
    }

        strcat(cmd, argv[1]);  
        system(cmd);

        return 0;
}

GOT THE ANSWER

int main(int argc, char* argv[]){
		char *d1;
		char *s;
		char d[50]="nslookup ";
		//d1=(char *)malloc(70);
		d1=argv[1];
		s=(char *)malloc(500);
		strcat(s,d);
		strcat(s,d1);
		printf("%s",s);	
		printf("\n");
		system(s);
		return 0;
}

[Elkvis]

you can't use strcat with your buffer unless you initialize it first. it will look for the first nul character, which may not be at index zero. it may not, in fact, be anywhere within the memory you allocated. you must, at minimum, set s[0] = 0 before calling strcat.