fscanf not reading char from file

Question

I have a program that reads from a file and converts assembly code into VM machine code. Instructions have different datatypes depending on the opcode, so my reader looks like this:

while(!feof(inF)) {
    fscanf(inF, "%s",&temp); //analyse first string and branch into if statement 
        printf("%s\n", temp);
        if (strcmp(temp, "NOP") == 0 || strcmp(temp, "nop") == 0) {
            fprintf(outF, "%i\n", 0);
        }
        else if (strcmp(temp, "LDI") == 0 || strcmp(temp, "ldi") == 0) {
            opcode = LDI; //opcode 1
            fscanf(inF," %c %d", &r1, &immediate); //get r1 and immediate
            printf("R1: %i\n", r1);
            printf("I: %i\n", immediate);
            r1 = getReg(r1);
            r2 = 0;
            subop = 0;
            output = (opcode << 27)|(r1 << 24)|(r2 << 21)|(subop << 16)|(immediate);
            fprintf(outF, "%x\n", output);
        }        
}

With a line reading LDI A 1024, I get an output of :

LDI
R1: 0
I: 1024

Instead of the expected

LDI
R1: 65
I: 1024

It appears that fscanf is not reading the char. I've looked at solutions that seemed to work for others and they don't seem to work here for some reason.

`fscanf(inF," %c %d", &r1, &immediate);` --> `fscanf(inF," %i %d", &r1, &immediate);` assuming `r1` is `int` — LPs, Feb 08 '17 at 07:46
A side note on why `while(!feof(inF))` is wrong: http://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong — ctrl-shift-esc, Feb 08 '17 at 08:00
Can you post a small complete example program demonstrating the issue, so that we can run it and check? — Marian, Feb 08 '17 at 08:15

score 1 · Accepted Answer · answered Feb 08 '17 at 08:26

1

You have declared the variable immediate as unsigned short while the line

fscanf(inF," %c %d", &r1, &immediate);

supposes it is an integer. The behavior is undefined in such cases.

answered Feb 08 '17 at 08:26

Marian

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I'll try changing the type and adding a cast to `unsigned short` after getting the value – parallel_resistance Feb 08 '17 at 14:52
Okay, this gets the desired result, but then it proceeds to give me the same result as above after returning the correct values for some reason. – parallel_resistance Feb 09 '17 at 06:14
Okay never mind I fixed that problem by adding a `return;` at the end of the if statement. – parallel_resistance Feb 09 '17 at 06:17

fscanf not reading char from file

1 Answers1