Stack Smashing error

**bisonbro42** · 02-15-2022

Does anyone know why my code has an error of "stack smashing detected"? And how I would go about fixing it? Thanks

Code:


#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

int main(void) {
   
   char abc[26];
   FILE* encryptFile;
   char code[1000];
   int form = 0;
   char ch;
   
   encryptFile = fopen("encrypted.txt", "r");
   do {
      ch = fgetc(encryptFile);
      code[form] = ch;
      form+=1;
   }
   while (ch != EOF);
   fclose(encryptFile);
   encryptFile = fopen("substitution.txt", "r");
   
   for(int i=0;i<26;i++){
      char ch = fgetc(encryptFile);
      abc[ch-97]=(char)(i+97);
   }
   
   fclose(encryptFile);
   encryptFile = fopen("decrypted.txt", "w");
   char first[form];
   for(int i=0; i<form-1;i++){
      ch = code[i];
      if(ch >= 97 && ch <= 122)
      first[i]=abc[ch-97];
      else if(ch >= 65 && ch <= 90){
         first[i]=toupper(abc[tolower(ch)-97]);
      }
      
      else 
      first[i]=ch;
      fprintf(encryptFile, "%c",first[i]);
   }
      
 
   return 0;
}

**Salem** · 02-15-2022

> char code[1000];
How big is encrypted.txt?
If it's more than 1000 chars, you have a problem.

> And how I would go about fixing it?
You don't need your code array, nor your first array.

Code:

FILE* encryptFile = fopen("encrypted.txt", "r");
FILE* decryptFile = fopen("decrypted.txt", "w");
int ch;
while ( (ch=fgetc(encryptFile)) != EOF ) {
    if(ch >= 97 && ch <= 122)
        ch=abc[ch-97];
    else if(ch >= 65 && ch <= 90){
        ch=toupper(abc[tolower(ch)-97]);
    }
    fputc(ch, decryptFile);
}

**hamster_nz** · 02-15-2022

I did a quick code review for you - see added comments.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>


int main(void) {


   char abc[26];
   FILE* encryptFile;
   char code[1000];
   int form = 0;
   char ch;


   encryptFile = fopen("encrypted.txt", "r");
   // You should check that the file has opened
   do {
      ch = fgetc(encryptFile);
      // If "encrypted.txt" is more than 1000 bytes, you will trash memory
      code[form] = ch;
      form+=1;
   }
   while (ch != EOF);


   fclose(encryptFile);


   encryptFile = fopen("substitution.txt", "r");
   // You should check that the file has opened


   for(int i=0;i<26;i++){
      char ch = fgetc(encryptFile);
      // If your file has any characters < 97 or > 97+26 you will trash memory
      abc[ch-97]=(char)(i+97); // Consider using characcter constants
   }


   fclose(encryptFile);
   encryptFile = fopen("decrypted.txt", "w");
   // You should check that the file has opened


   char first[form];
   for(int i=0; i<form-1;i++){  // You most probably want "i<form", not "i<form-1"
      ch = code[i];
      if(ch >= 97 && ch <= 122) // Consider using character constants here
      first[i]=abc[ch-97];
      else if(ch >= 65 && ch <= 90){ // Consider using character constants
         first[i]=toupper(abc[tolower(ch)-97]); // Consider using chacter constants
      }


      else
      first[i]=ch;
      fprintf(encryptFile, "%c",first[i]);
   }


   return 0;
}

Also there are some weird indentation in the last loop. It would pay to make the nesting clear.

**john.c** · 02-16-2022

Code:

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
 
void init_alpha(char *alpha)
{
    const char *filename = "substitution.txt";
    FILE *fin = fopen(filename, "r");
    if (!fin)
    {
        perror(filename);
        exit(EXIT_FAILURE);
    }
 
    memset(alpha, '-', 26);
 
    for (int i = 0; i < 26; ++i)
    {
        int ch = fgetc(fin);
        if (ch == EOF)
        {
            fprintf(stderr, "Error: less than 26 chars in subsitution file.\n");
            exit(EXIT_FAILURE);
        }
 
        if (ch >= 'a' && ch <= 'z')
            alpha[ch - 'a'] = i + 'a';
        else if (ch >= 'A' && ch <= 'Z')
            alpha[ch - 'A'] = i + 'a';
        else
        {
            fprintf(stderr, "Error: bad character in substitution file.\n");
            exit(EXIT_FAILURE);
        }
    }
    fclose(fin);
 
    if (memchr(alpha, '-', 26))
    {
        fprintf(stderr, "Error: not all characters in substitution file.\n");
        exit(EXIT_FAILURE);
    }
}
 
int main()
{
    const char *filein  = "encrypted.txt";
    const char *fileout = "decrypted.txt";
 
    char alpha[26];
    init_alpha(alpha);
 
    FILE *fin = fopen(filein, "r");
    if (!fin)
    {
        perror(filein);
        exit(EXIT_FAILURE);
    }
 
    FILE *fout = fopen(fileout, "w");
    if (!fout)
    {
        perror(fileout);
        exit(EXIT_FAILURE);
    }
 
    for (int ch; (ch = fgetc(fin)) != EOF; )
    {
        if (ch >= 'a' && ch <= 'z')
            ch = alpha[ch - 'a'];
        else if (ch >= 'A' && ch <= 'Z')
            ch = toupper(alpha[ch - 'A']);
 
        fputc(ch, fout);
    }
 
    fclose(fout);
    fclose(fin);
    return 0;
}

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