CODEWITHSUNDEEP
clinuxparameter-passing
Jonathan
Jonathan

Reputation: 608

how to pass int/char into system() a Linux system call

Ok it might sounds dumb, but I couldn't figure out a way to pass int/char into this system call

here is how I would like it to work 

system ("cal %d %d", month, year);

I expect this will give me the following command on terminal "cal 3 2009"

and the terminal will show me the calendar of March 2009.

But the compiler is complaining it has too many arguments

any ideas? I need to make this method system ("cal ") return me a dynamic calendar.

Notes: cal take the argument cal month year

Upvotes: 4

Views: 5479

Answers (7)

unwind
unwind

Reputation: 399813

You need to build the proper command line string, system() won't do it for you:

char cmd[64];

snprintf(cmd, sizeof cmd, "cal %d %d", month, year);
system(cmd);

The usual caveats about buffer overflow apply, although in this particular case when both arguments are integers you should be fairly safe.

Upvotes: 8

yves Baumes
yves Baumes

Reputation: 9026

try

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

int main()
{
  char command_buf [20];
  const int month = 3;
  const int year = 2009;
  snprintf(command_buf, sizeof(command_buf), "cal %d %d", month, year);
  system(command_buf);
}

Upvotes: 1

shodanex
shodanex

Reputation: 15406

Basically, just do your printf thing out of the system call :

char my_cmd[MAX_SIZE];
snprintf(my_cmd, MAX_SIZE, "cal %d %d", month, year);
system(my_cmd);

Upvotes: 3

user82238
user82238

Reputation: 

char
  string[64];

sprintf( string, "cal %d %d", month, year );

system( string );

Upvotes: 0

Stefano Borini
Stefano Borini

Reputation: 143795

This happens because you are assuming system behaves like printf, which is not the case. To obtain what you need, you have first to obtain the substitution through sprintf into a buffer, then pass this buffer to system.

Be careful though, this can become a potential security hole, because you are potentially allowing unknown parameters to be passed at command line execution. Also, you have to be careful that the temporary buffer you use is large enough to host your final string.

Upvotes: 1

fa.
fa.

Reputation: 2486

you have to format your command in a string before calling system with it, use snprintf for instance

Upvotes: 0

sharptooth
sharptooth

Reputation: 170499

You need to pass a string that already has all necessary transformations made. You can use sprintf() for producing such a string, just be careful with allocating a large enough buffer.

Upvotes: 1

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