Finding source of garbage value

Question

So I've made a custom code to remove spaces from a string. But when I ran it, if there's no input, the second string will give 3 garbage values, and if there are too many spaces, the code will sometimes add a space string on its own. I just can't find where the three garbage values come from :(

#define SIZE 200
int main ()
{
    int w=0, z=0, x=0, y=0, z0, rDlength=0, Dlength=0, RandomChar, Dx=0, Dy=0;
    char rstring[SIZE], string[SIZE];
    srand(time(NULL));

    //debug
    int space=0;

    printf("Input Text: ");
    gets(rstring);
    strupr(rstring);
    strlen(rstring);
    rDlength=strlen(rstring);

    //debug
    printf("%d\n", rDlength);

    w=-1; 
    for(z=0;z<=rDlength;z++)
    {    if(rstring[z]==' ')
         {   space++;
             continue;
         }
         else if(rstring[z]=='\0')
             break;
         else if(rstring[z]!=' ')
             string[++w]=rstring[z];
    }

    //debug
    printf("%d\n", space);

    Dlength=strlen(string);

    for(z=0;z<rDlength;z++)
        printf("%c", rstring[z]);
    printf("\n");

    for(z=0;z<Dlength;z++)
        printf("%c", string[z]);
    printf("\n");

    printf("String length is %d\n", Dlength);
    return 0;
}

If there's at least 3 input characters, then the garbage value seem to disappear. but if there's only two or one character, then the garbage values appear.

The code is unreadable. Format&indent it properly. Don't get too creative with formatiing. — too honest for this site, Sep 26 '16 at 16:59
You have not terminated `string` the array you are copying char by char to. So `Dlength=strlen(string);` will not give the right answer. — Weather Vane, Sep 26 '16 at 17:00
Oh, Sorry Olaf, I'm very new on this site. What do you mean by indent and format, if I may ask? — Felix Wright, Sep 27 '16 at 16:24

score 2 · Accepted Answer · answered Sep 26 '16 at 17:06

When you add characters to string, you aren't adding a terminating null character. So any elements of string past that are uninitialized. Calling strlen then reads those uninitialized characters resulting in undefined behavior.

After copying the characters, add the null terminator to the end:

for(z=0;z<=rDlength;z++) {
    if(rstring[z]==' ') {
        space++;
        continue;
    }
    else if(rstring[z]=='\0')
        break;
    else if(rstring[z]!=' ')
        string[++w]=rstring[z];
}
string[++w]='\0';

Oh my, I didn't notice that at all!! Thank you so much!, the code is working well now! Bless you! :D — Felix Wright, Sep 27 '16 at 16:28

Finding source of garbage value

1 Answers1