Multiple calls of fread make the program acting abnormally

Question

Thank you for all advices, I solved the problem and it is function call overflow. Yes, the code is really a mass and ugly so I managed to clean it up, I will replace the code with the new one here.

This is my final year project, I am trying to write a c program that reads multiple .c codes and modifying it, then complie and running it and finally reads the ouput.txt and comparing it with ans.txt.

I am encountering a weird problem, the code complies with no warning, but when I tried to run it at command line, it does nothing but shows a empty line.

After few testing, I find that if I comment one line of code, that is a call of fread function, the program will works fine. I do not understand the reason and how to solve it.

when the program works, it should be like this in command line:
C:\batch.exe
Welcome to the batch system
(Starts processing)...

However, I am getting this now:
C:\batch.exe

C:\

here is my the main part of my code:

int main(){
int agu = 1, fim;   // agument for controlling the program
int filesize[256];         //used on sacn()
int num = 0;                    // stores total number of files detected         
char sdir[] = "./input/", filter[]= "*.c", filename[128][256];       //Varibies used on auto-detecting
struct _finddata_t c_file;                   //Varibies used on auto-detecting
long hFile;                                  //Varibies used on auto-detecting
printf("\nWelcome to the my system");
Sleep(1000);
printf("\nPlease put all files on input folder in order to let this program read it");
Sleep(1000);
fflush(stdout);
do{                       
    _chdir(sdir);
    hFile = _findfirst(filter, &c_file);
    if (hFile != -1)
    {
        num = 0;
        do{
            sprintf(filename[num], "%s", c_file.name);
            printf("\n%s\n", filename[num]);
            num++;
        } while (_findnext(hFile, &c_file) == 0);

    }
    else{
        printf("\nNo .c files found in input folder.\nThe Program will be exit after 5 second.");
        Sleep(5000);
        return 0;
    }
    _chdir("..");
    printf("\nTotal %d file(s) will be imported", num);
    printf("\nConfirm ? (Y / N)\nYou Can Also Press Ctrl + C or Enter Q to Terminate this Program.");
    do {
        fim = getchar();
        putchar(fim);
        if (fim == 'Y' || fim == 'y')
            agu = 0;
        else if (fim == 'Q' || fim == 'q')
            return 0;
        else agu = 1;
    } while (fim != 'y' && fim != 'Y' && fim != 'N' && fim != 'n');


}while(agu==1);
mod(filename,sdir,num);  // modify , compile and run the code
printf("\nEnter Y to Start Result Comparing, or Enter N to Exit This Program.(Y/N)");
fim = 'a';
do {
    fim = getchar();
    putchar(fim);
    if (fim == 'Y' || fim == 'y')
        agu = 0;
    else agu = 1;
} while (fim != 'y' && fim != 'Y' && fim != 'N' && fim != 'n');

if (agu == 0){      //Resulting Comparing Function
    comp();
}
else{
    printf("\nThank You For Using This Software, This Program will be terminated.");
}
return 0;
 }

Answer 1

The printf() for filebuff[x] might print lots of (invisible) garbage due to a buffer overflow:

fread() returns the file content without trailing '\0'. Thus you get a buffer overflow, e.g. in the printf() after fread() and later in strlen() and scan(). There are two (or probably more) solutions:

• Set a null delimiter at the end of the file content immediately after the call to fread():

  filebuff[x][fsize]='\0'
  

  before accessing the buffer as C-string.

• Make a separate array of file-sizes for each file:

  int filesize[256]; filesize[x] = fsize; 
  

  and use this size later on in scan()

Other problems that caught my eyes:

• sizeof(char[xxx]) always returns the size of the buffer, not the string-length of its content. Thus

  sizeof(filebuff[x])   // always returns 2048
  sizeof(inputFiles[x]) // always returns 10 
  

• In function scan():

  if (input[curr] == 'p' && 
      input[curr + 1] == 'r' &&
      input[curr + 2] == 'i' &&
      input[curr + 3] == 'n' &&
      input[curr + 4] == 't' &&
      input[curr + 5] == 'f'
  )
  

  has a potential buffer overflow as well: If you reached nearlly the end of file input[curr + 5] reads past the end of your content. Better use strstr() instead.

Answer 2

stdout is row buffered. If you print stuff without an ending \n you need to flush stdout.

printf("\nWelcome to the batching system");
fflush(stdout);  // Added line
Sleep(1000);

Right now, your program is waiting for input, but you don't realize it is, because the prompt text is still in the print buffer.