CODEWITHSUNDEEP
cstringpointers
shailendra
shailendra

Reputation: 271

System command in C, how to pass a pointer inside a string enclosed inbetween ""

I am trying to use system command in a C code where i want to execute gzip -r command to convert a .txt file to .txt.gz.Now the name of the file to be converted is stored in a pointer and as per documentation provided at this link, we need to copy the whole command of gzip like this to a string

char gzip[100];
strcpy(gzip,"gzip -r /home/abc/xyz/pqr.txt");

now i have a problem here, name of file pqr.txt is stored in a pointer.So how can i pass that pointer to the string which is being copied in gzip and then is passed to the system command.

Here is the full code which i am using.

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

int main()
{ char *ptr1= "gzip -r/home/shailendra/sampleprograms/C/output.txt";  //working
  //char *ptr2 = "/home/shailendra/sampleprograms/C/output.txt"; // pointer used tyo store th name of file
  //char *ptr =  " gzip -r *ptr2.sstv";  //not working
int i;
char tar[50];
system(ptr1); //working
system(ptr);  //not working
return 0;
}

so instead of first initializing an array and then copying the string to array and then passing to system command i passed the string to a pointer and then pass that pointer to the system command.

So my main concern is how i can pass the name of the file which is stored in some pointer to the string, so that it is processed by system command

Upvotes: 0

Views: 470

Answers (2)

undur_gongor
undur_gongor

Reputation: 15954

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

int 
main(void)
{
    const char *file = "/home/shailendra/sampleprograms/C/output.txt";

    char buf[500];

    if (snprintf(buf, sizeof buf, "gzip -r '%s'", file) >= sizeof buf) {
        /* command could not be composed, too long */
    } else {
        system(buf); 
    }

    return 0;
}

Upvotes: 0

Klas Lindb&#228;ck
Klas Lindb&#228;ck

Reputation: 33273

Simply combine the two into one string. sprintf can help you:

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

int main()
{
  char *ptr2 = "/home/shailendra/sampleprograms/C/output.txt"; // pointer used tyo store th name of file
  char *ptr =  " gzip -r '%s'"; 
  int i;
  char buf[500];
  sprintf(buf, ptr, ptr2);
  system(buf); //working
  return 0;
}

Upvotes: 1

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