How do I read hex numbers into an unsigned int in C

Question

I\'m wanting to read hex numbers from a text file into an unsigned integer so that I can execute Machine instructions. It\'s just a simulation type thing that looks inside

Answer 1

You're on the right track. Here's the problems I saw:

• You need to exit if fopen() return NULL - you're printing an error message but then continuing.
• Your loop should terminate if i >= 80, so you don't read more integers than you have space for.
• You need to pass the address of num[i], not the value, to fscanf.
• You're calling fscanf() twice in the loop, which means you're throwing away half of your values without storing them.

Here's what it looks like with those issues fixed:

#include 

int main() {
    FILE *f;
    unsigned int num[80];
    int i=0;
    int rv;
    int num_values;

    f=fopen("values.txt","r");
    if (f==NULL){
        printf("file doesnt exist?!\n");
        return 1;
    }

    while (i < 80) {
        rv = fscanf(f, "%x", &num[i]);

        if (rv != 1)
            break;

        i++;
    }
    fclose(f);
    num_values = i;

    if (i >= 80)
    {
        printf("Warning: Stopped reading input due to input too long.\n");
    }
    else if (rv != EOF)
    {
        printf("Warning: Stopped reading input due to bad value.\n");
    }
    else
    {
        printf("Reached end of input.\n");
    }

    printf("Successfully read %d values:\n", num_values);
    for (i = 0; i < num_values; i++)
    {
        printf("\t%x\n", num[i]);
    }

    return 0
}