When using printf, newline makes string disappear

Question

I am writing a program that takes an input file that consists of drawings of characters made up of hashtags (A, B, C...), reads a string from a console and prints out that string by drawing the characters according to the input file.

Note: As you will see below, the input file contains '.' instead of spaces. These are replaced with spaces in my code.

For some reason when I print a newline after a character is drawn, pieces of the character disappear.

I know it sounds complicated so I will provide all the file and the output below.

Here is the code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
typedef struct{
    char znak[5][5 + 1];
} slovo;

void napuni(slovo *znakovi, FILE *ulaz);

int main(){
    int i,j;
    FILE *ulaz = fopen("ascii.in", "r");
    slovo *znakovi = calloc(27, sizeof(slovo));
    napuni(znakovi, ulaz);
    fclose(ulaz);
    FILE *izlaz = fopen("ascii.out", "w");
    char *tekst = calloc(50,sizeof(char));
    fgets(tekst,50,stdin);
    char *znak = strchr(tekst, '#');
    *znak = '\0';
    int duljina = strlen(tekst);
    for (j = 0; j < 5; j++){
        for (i = 0; i < duljina; i++){
                int znak2 = toupper(tekst[i]) - 65;
                fprintf(izlaz, "%s", znakovi[znak2].znak[j]);
        }
        fprintf(izlaz,"\n");
    }
    fclose(izlaz);
    return 0;
}

void napuni(slovo *znakovi, FILE *ulaz){
    char redak[6];
    int i,j;
    for (i = 0; i < 27; i++){

        for (j = 0; j < 7; j++){
            if (feof(ulaz)) break;
            fgets(redak,6,ulaz);
            if (redak[0] == '\n' || redak[0] == 32) continue;
            char *znak = strchr(redak, '.');
            while(znak != NULL){
                *znak = 32;
                znak = strchr(redak,'.');
            }
            strcpy(znakovi[i].znak[j], redak);
            printf("\n%s",znakovi[i].znak[j]); // this line prints the character to console for testing
        }
        printf("\n"); //when this line is uncommented pieces of the character disappear
    }
}

Here is the input file:

..#..
.#.#.
.###.
.#.#.
.#.#.

.##..
.#.#.
.##..
.#.#.
.##..

..#..
.#.#.
.#...
.#.#.
..#..

.##..
.#.#.
.#.#.
.#.#.
.##..

.###.
.#...
.##..
.#...
.###.

.###.
.#...
.##..
.#...
.#...

..#..
.#...
.#.##
.#..#
..##.

.#.#.
.#.#.
.###.
.#.#.
.#.#.

..#..
..#..
..#..
..#..
..#..

...#.
...#.
...#.
.#.#.
..#..

.#.#.
.#.#.
.##..
.#.#.
.#.#.

.#...
.#...
.#...
.#...
.###.

#...#
##.##
#.#.#
#...#
#...#

#..#.
##.#.
#.##.
#..#.
#..#.

..#..
.#.#.
.#.#.
.#.#.
..#..

.##..
.#.#.
.##..
.#...
.#...

..#..
.#.#.
.#.#.
.#.#.
..##.

.##..
.#.#.
.##..
.##..
.#.#.

..##.
.#...
.###.
...#.
.##..

.###.
..#..
..#..
..#..
..#..

.#.#.
.#.#.
.#.#.
.#.#.
.###.

.#.#.
.#.#.
.#.#.
.#.#.
..#..

#...#
#...#
#.#.#
#.#.#
.#.#.

#...#
.#.#.
..#..
.#.#.
#...#

.#.#.
.#.#.
.###.
...#.
..##.

.###.
...#.
..#..
.#...
.###.

..#..
.#.#.
...#.
..#..
..#..

Here is a test output (just printing out each character one at a time) when I don't insert a newline character in between:

  #
 # #
 ###
 # #
 # #
 ##
 # #
 ##
 # #
 ##
  #
 # #
 #
 # #
  #
 ##
 # #
 # #
 # #
 ##
 ###
 #
 ##
 #
 ###
 ###
 #
 ##
 #
 #
  #
 #
 # ##
 #  #
  ##
 # #
 # #
 ###
 # #
 # #
  #
  #
  #
  #
  #
   #
   #
   #
 # #
  #
 # #
 # #
 ##
 # #
 # #
 #
 #
 #
 #
 ###
#   #
## ##
# # #
#   #
#   #
#  #
## #
# ##
#  #
#  #
  #
 # #
 # #
 # #
  #
 ##
 # #
 ##
 #
 #
  #
 # #
 # #
 # #
  ##
 ##

As you can see it behaves as expected. However if I insert a newline character in between, the characters get mangled up. See below:

  #
 # #
 ###
 # #

 # #
 ##
 # #

 ##
 # #
 ##

  #
 # #
 #

 # #
  #
 ##

 # #
 # #
 # #
 ##

 ###
 #
 ##

 #
 ###
 ###

 #
 ##
 #

 #
  #
 #

 # ##
 #  #
  ##

 # #
 # #
 ###
 # #

 # #
  #
  #

  #
  #
  #

   #
   #
   #

 # #
  #
 # #

 # #
 ##
 # #
 # #

 #
 #
 #

 #
 ###
#   #

## ##
# # #
#   #

#   #
#  #
## #

# ##
#  #
#  #

  #
 # #
 # #
 # #

  #
 ##
 # #

 ##
 #
 #

  #
 # #
 # #

 # #
  ##
 ##

That's basically it. I am a beginner in C so any help is appreciated.

Unrelated suggestion: Code in English - always! Pretty much every programmer understands it and if you don't anyone besides your countrymen will have a harder time understanding your code. (I'm German and I hate seeing German code!) — ThiefMaster
– ThiefMaster, Commented Jan 10, 2016 at 10:33
redak[6] = '\0'; invokes UB. Remove it as fgets does the job automatically. — Spikatrix
– Spikatrix, Commented Jan 10, 2016 at 10:35
Try if (redak[0] == '\n' || redak[0] == 32) continue; → if (redak[0] == '\n' || redak[0] == 32) {j--; continue;} — Spikatrix
– Spikatrix, Commented Jan 10, 2016 at 10:41
If that did not work, try changing for (j = 0; j < 5; j++){ for (i = 0; i < duljina; i++){ to for (i = 0; i < duljina; i++){ for (j = 0; j < 5; j++){ — Spikatrix
– Spikatrix, Commented Jan 10, 2016 at 10:52

kfx · Accepted Answer · 2016-01-10 10:58:50Z

1

You have a buffer overflow error in your code. You declare redak as:

char redak[6];

And then overwrite memory past the end of it with this line:

redak[6] = '\0';

The result is an undefined behavior. Note that tools like valgrind would help to catch this kind of errors easily.

Another problem is with your for loop: the condition should be j<6 instead of 7.

Finally, redak should be of size 7 and the fgets() changed accordingly. Otherwise fgets does not read the newline character in, and so you start reading the "next" line from the wrong position. Remember that fgets reads maximally one less than size characters.

This all also means that char znak[5][5 + 1] should be changed to char znak[6][7].

edited Jan 10, 2016 at 10:58

answered Jan 10, 2016 at 10:37

kfx

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2 Comments

isaric Over a year ago

I have commented out that line but the output remains the same.

Tom Karzes Over a year ago

There are more problems than just this. There are other array index errors.

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