CODEWITHSUNDEEP
c
zenpoy
zenpoy

Reputation: 20126

Making a C program smaller

I have a very small C program which reverses a file. It compiles on windows to an exe file of size 28,672 bytes.

BTW - when compiled with gcc I get around 50Kb file and when compiled with cl I get 28Kb.

EDIT: Here is the code

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

int main(int argc, char *argv[])
{
   FILE *fi, *fo;

   char *file1, file2[1024];
   long i, length;
   int ch;

   file1 = argv[1];

   file2[0] = 0;
   strcat(file2, file1);
   strcat(file2, ".out");

   fo = fopen(file2,"wb");
   if( fo == NULL )
   {
      perror(file2);
      exit(EXIT_FAILURE);
   }

   fi = fopen(file1,"rb");
   if( fi == NULL )
   {
      fclose(fo);
      return 0;
   }

   fseek(fi, 0L, SEEK_END);
   length = ftell(fi);
   fseek(fi, 0L, SEEK_SET);

   i = 0;
   while( ( ch = fgetc(fi) ) != EOF ) {
      fseek(fo, length - (++i), SEEK_SET);
      fputc(ch,fo);
   }

   fclose(fi);
   fclose(fo);
   return 0;
}

UPDATE:

Upvotes: 6

Views: 4777

Answers (4)

Tim
Tim

Reputation: 5691

Which libraries do you use? You don't need any libraries for reversing a file in C except the standard lib. Then your executable should be no larger than 2kb.

However if I compile:

int main()
{
    return 0;
}

with MinGW, the size of the executable is equal to 48kb. But I haven't used any optimalization flags.

Edit: With the -s flag, it reduces to 7,5 kb.

Upvotes: 1

Jack
Jack

Reputation: 16724

Check out -s gcc flag:

-s Remove all symbol table and relocation information from the executable.

A test with small C program that I'm developing:

Without -s: 120,2 Kib

With -s: 58,3 Kib

By removing dead code from your executable:

By using -fdata-sections -ffunction-sections the compiler will put the unused function into separed section that by using -Wl,--gc-sections will be removed by the `link.

The file size now is: 50,2 Kib

By -O2

do a lot of optimizations, but without increase file size, usually, unlike.

The file size now is: 42,1 KiB

gcc there is too some -O* to optimization in favor to file size.

Upvotes: 2

DevSolar
DevSolar

Reputation: 70313

#include <stdio.h>

Let it be said by someone who implemented his own version of the stdio functions: They are quite big, and somewhat interdependent. Linking one of them links in several others automatically.

Since this is a one-time cost, and doesn't matter in the scope of big applications, most libraries don't bother much with optimizing this away.

That being said, compiling into a dynamically linking executable instead of a static one is usually the way to go. If you have to have a statically linked executable, you might want to look at one of the libraries optimized for embedded environments, as they are more focussed on small-size optimizations like this.

Upvotes: 3

alinsoar
alinsoar

Reputation: 15803

Try to compile it using tcc: http://bellard.org/tcc/ .

Upvotes: 8

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