C

C Programming Language

Purpose:

Example of using C on the Harvard University FAS cluster. The specific example compute the integer sum from 1 to N, where N is a number read from the command line.

Contents:

• sum.c: C source code
• run.sbatch: Example batch-job submission script
• c_test_job.out: STD output file

Compile:

Request a compute node on the test partition, e.g.:

salloc -p test --nodes=1 --cpus-per-task=2 --mem=4GB --time=0-01:00:00

Compile the code. In this example, we will use the GNU compiler, e.g:

module load gcc/9.5.0-fasrc01
gcc -O2 -o sum.x sum.c

C source code:

//====================================================================
// Program: sum.c
//          Computes integer sum from 1 to N where N is an integer
//          read from the command line
//
// Compile: gcc -O2 -o sum.x sum.c
//
// Usage:   ./sum.x N
//====================================================================
#include <stdio.h>
#include <stdlib.h>

// Main program.......................................................
int main(int argc, char *argv[] ){
  int i;
  int j;
  int n;
  n = atoi( argv[1] );
  printf("%s %d \n", "Welcome! This program prints out the sum of 1 to", n);
  j = 0;
  for ( i = 1; i <= n; i++ ){
    j = j + i;
  }
  printf("%s %d %s %d \n", "Sum of 1 to", n, "is", j);
  printf("%s \n", "End of program.");
  return 0;
}

Example batch-job submission script:

In this example, we will use the same GNU compiler version used at the time of compilation for launching our production run.

#!/usr/bin/env bash
#SBATCH -J c_test_job
#SBATCH -o c_test_job.out
#SBATCH -e c_test_job.err
#SBATCH -p shared
#SBATCH -N 1
#SBATCH -c 1
#SBATCH -t 0-00:30
#SBATCH --mem=2G

# Load required software modules
module load gcc/9.5.0-fasrc01

# Run program
./sum.x 100

Submit job:

sbatch run.sbatch

Example output:

$ cat c_test_job.out
Welcome! This program prints out the sum of 1 to 100 
Sum of 1 to 100 is 5050 
End of program.