Why am I getting garbage characters?

Question

I keep getting garbage characters when I am outputing "123" and "0".

I was able to narrow it down to the baseout method, and I believe it may be one of my "for loop" conditions but I can't seem to get to be able to remove the garbage characters.

If you can help, please do. Program is in C.

Thank you in advance.

#include <stdio.h>

#define COUNT 8     /* number of hex digits to display */
#define DECIMAL 10  /* to indicate base 10 */
#define HEX 16      /* to indicate base 16 */

/* array used for ASCII conversion */
const char digits[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

void baseout (int number, int base, FILE * stream) {
int f1;
int f2;
int index = 0;
int result = number;
char store1[f2];

/*This condition outputs the digit "0" on Line 4*/
if (number == 0) {          
    fputc(digits[0], stream); 
}

/*This condition outputs the digit "0" after "0x"*/
if (base != DECIMAL){
    store1[f1] = '0';
    fputc(store1[f1], stream);

}

/*This condition outputs codes from bases 2-36*/
if (number != 0) {
   for(f2 = 1; f2 < COUNT && result != 0; f2++){
      index = result % base;
      store1[f2] = digits[index];
      result = result / base;
   }
}

for (f2 = COUNT; f2 > 0; f2--){
    fputc(store1[f2], stream);
}
}

void decout (unsigned int number, FILE * stream) {
    /*Passes DECIMAL to baseout algorithm*/
    baseout(number, DECIMAL, stream);    
}

void hexout (unsigned int number, FILE * stream) {

    /* Output "0x" for hexidecimal. */
    writeline ("0x", stream);
    baseout (number, HEX, stream);
}
void newline (FILE * stream) {
    /* Output a newline character */
    fputc('\n', stream);  
}
int writeline (const char * message, FILE * stream) {
    int index = 0;  
    /*While "index<messagelength" output the each character of message*/
    while(message[index] != '\0'){
            fputc(message[index], stream);
        index++;
    }
    /*Return the message length*/
    return sizeof(message); 
}


int main (int argc, char *const* argv) {
    writeline ("Hello World", stdout);
    fprintf (stderr, "Hola Mundo\n");
    newline(stdout);
    decout (123, stdout);
    newline(stdout);
    decout (0, stdout);
    newline(stdout);
    hexout (0xFEEDDAD, stdout);
    newline(stdout);
    return 0;
}

The Desired Output is:

Hola Mundo

Hello World

123

0

0x0FEEDDAD

The Current Output is:

Hola Mundo

Hello World

123

0123

0x0FEEDDAD

Try focusing on one issue at a time. Reduce the code to a small test case of just one issue and debug it, then when that is working move on to the next issue. — Retired Ninja, Oct 14 '14 at 21:12
`for (f1 = COUNT - 1; f1 < COUNT; f1++)` makes the body of the loop always execute exactly once. If this is the intention, it should be rewritten without a loop construct — iwolf, Oct 14 '14 at 21:14
What exactly is desired output and actual output of your program? — Anton Savin, Oct 14 '14 at 21:15
BTW `return sizeof(message);` returns always the same `sizeof(char*)`, that is 4 or 8, though luckily it's not used anywhere in your code. — Anton Savin, Oct 14 '14 at 21:21
Note: `index = result % base;` will result in a negative `index` if `number < 0`. — chux - Reinstate Monica, Oct 14 '14 at 22:37
@AntonSavin I edited the post to show desired output. I was able to get rid of the garbage but ran into another problem. Extra 123 — ml_practice, Oct 14 '14 at 22:55

score 1 · Answer 1 · answered Oct 14 '14 at 21:18

Your array store1 in the function baseout is not initialized. Your function does not populate every element in that array, resulting in garbage being left in some of the higher elements. One solution is to initialize the array to all spaces (or zeros or whatever character you want) at the start of the function:

for(index = 0; index < COUNT ; index++)
{
    store1[index] = ' ';
}

Another possibility is to remove the "if (result != 0)" check in your baseout function (around line 34). This will store zero in the store1 array for every element that has a zero. This will result in printing "0000123" instead of " 123"

score 1 · Accepted Answer · answered Oct 14 '14 at 21:35

This block of code is not well thought out.

    for(f2 = 1; f2 < COUNT; f2++){
        if (result != 0){
            index = result % base;
            store1[f2] = digit[index];
            result = result / base;
        }
    }

You are incrementing f2 even after result is 0 and not setting the value of store1[f2] for those values. Then you go ahead and try to print the contents of store1. Since store1 is not initialized to anything sensible, you are getting garbage.

Here's one way to fix those problems.

/*This condition outputs codes from bases 2-36*/
if (number != 0) {
   for(f2 = 1; f2 < COUNT && result != 0; f2++){
      index = result % base;
      store1[f2] = digits[index];
      result = result / base;
   }               
}

for (f2--; f2 > 0; f2--){
    fputc(store1[f2], stream);
}

Thank you. I was able to get rid of the garbage but now I ended up producing an extra 123. I editted the code I posted above to the new code. There is something wrong with the for condition still. Also the f2-- as the initial condition for the for loop still causes garbage so I had to set it to COUNT. — ml_practice, Oct 14 '14 at 22:47
@BrianLeung, not sure what you did. I get reasonable output. Checkout working code at http://ideone.com/pOZEWS. — R Sahu, Oct 15 '14 at 02:42

Why am I getting garbage characters?

2 Answers2