c fscanf for ints causes segfault

Question

DISCLOSURE: This is homework.

The code below is meant to read a command file formatted like:

ADD 6 6 5
ADDTERM 0 1 1
MULTIPLY 2 40

and call the appropriate command using the given parameters. For some reason, while ADD and ADDTERM work as expected, I get a segfault when the multiply line is read.

    int arg_1 = 0, arg_2 = 0, arg_3 = 0;

    while(fscanf(commands, "%s", command) != EOF)
    {
            if(strcmp(command, "ADDTERM") == 0)
            {
                    /*The following line runs fine!*/
                    fscanf(commands, "%d %d %d",
                                    &arg_1, &arg_2, &arg_3);
                    printf("ADDTERM, Poly: %d, Coeff: %d, Exp: %d\n",
                                    arg_1, arg_2, arg_3);
                    if(polys[arg_1] == NULL)
                    {polys[arg_1] = CreatePolynomial();}
                    AddTermToPoly(polys[arg_1], arg_2, arg_3);
            }

            else if(strcmp(command, "MULTIPLY") == 0)
            {
                    /*The following line results in a segfault*/
                    fscanf(commands, "%d %d", &arg_1, &arg_2);

                    printf("MULTIPLY, Poly: %d, Multiplier: %d\n",
                                    arg_1, arg_2);
                    MultiplyPoly(polys[arg_1], arg_2);
            }

            /*...*/  
   }

This is also only a problem on my school's Linux server. My home computer runs it just fine, using "gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5)", whereas my school uses "gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)"

Any ideas why this would be? Your help is appreciated!

Answer 1

You need to leave room for a null terminus '\\0' in your string. You were okay with ADDTERM because it has 1 less letter than MULTIPLY.