optimization - GCC C++ "Hello World" program -> .exe is 500kb big when compiled on Windows. How can I reduce its size?

Question

I just recently started learning C++ - I am using nuwen's version of MingW on Windows, using NetBeans as an IDE (I have also MSDN AA Version of MSVC 2008, though I don't use it very often).

When compiling this simple program:

#include <iostream>
using namespace std;

int dog, cat, bird, fish;

void f(int pet) {
  cout << "pet id number: " << pet << endl;
}

int main() {
  int i, j, k;
  cout << "f(): " << (long)&f << endl;
  cout << "dog: " << (long)&dog << endl;
  cout << "cat: " << (long)&cat << endl;
  cout << "bird: " << (long)&bird << endl;
  cout << "fish: " << (long)&fish << endl;
  cout << "i: " << (long)&i << endl;
  cout << "j: " << (long)&j << endl;
  cout << "k: " << (long)&k << endl;
} ///:~

my executable was about 1MB big. When I changed project configuration from Debug to Release, used -O1 -Os flags ( stripping debugging symbols along the way ), binary size was reduced from 1MB to 544KB.

I am not a "size freak", but I am just wondering - is there any way, that I could reduce .exe size even more? I just think, that 544KB is just too much for such a simple application ).

Answer 1

The problem here is not so much with the library as it is with the way the
library is linked. Granted, iostream is a moderately huge library but I don't
think it can be so huge as to cause a program to generate an executable that is
900KB larger than a similar one that uses C functions. The one to blame
is not iostream but gcc. More accurately, static linking is to be blamed.

How would you explain these results(with your program):

g++ test.cpp -o test.exe              SIZE: 935KB
gcc test.cpp -o test.exe -lstdc++     SIZE: 64.3KB

Different sizes of executables are being generated with exactly the same
build options.

The answer lies in the way gcc links the object files.
When you compare the outputs from these two commands:

g++ -v test.cpp -o test.exe // c++ program using stream functions  
gcc -v test.c -o test.exe   // c program that using printf  

you'll find out that the only places they differ(apart from the paths to the
temporary object files) is in the options used:

   C++(iostream) | C(stdio)
-------------------------------
-Bstatic         |  (Not There)
-lstdc++         |  (Not There)
-Bdynamic        |  (Not There)
-lmingw32        | -lmingw32 
-lgcc            | -lgcc 
-lmoldname       | -lmoldname 
-lmingwex        | -lmingwex 
-lmsvcrt         | -lmsvcrt 
-ladvapi32       | -ladvapi32 
-lshell32        | -lshell32 
-luser32         | -luser32 
-lkernel32       | -lkernel32 
-lmingw32        | -lmingw32 
-lgcc            | -lgcc 
-lmoldname       | -lmoldname 
-lmingwex        | -lmingwex 
-lmsvcrt         | -lmsvcrt 

You've got your culprit right there at the top. -Bstatic is the option that comes
exactly after the object file which may look something like this:

"AppData\Local\Temp\ccMUlPac.o" -Bstatic -lstdc++ -Bdynamic ....

If you play around with the options and remove 'unnecessary' libraries,
you can reduce the size of the executable from 934KB to 4.5KB max
in my case. I got that 4.5KB by using -Bdynamic, the -O flag
and the most crucial libraries that your application can't live without, i.e
-lmingw32, -lmsvcrt, -lkernel32. You'll get a 25KB executable at that
point. Strip it to 10KB and UPX it to around 4.5KB-5.5KB.

Here's a Makefile to play with, for kicks:

## This makefile contains all the options GCC passes to the linker
## when you compile like this: gcc test.cpp -o test.exe
CC=gcc

## NOTE: You can only use OPTIMAL_FLAGS with the -Bdynamic option. You'll get a
## screenfull of errors if you try something like this: make smallest type=static
OPTIMAL_FLAGS=-lmingw32 -lmsvcrt -lkernel32

DEFAULT_FLAGS=$(OPTIMAL_FLAGS) 
-lmingw32 
-lgcc 
-lmoldname 
-lmingwex 
-lmsvcrt 
-ladvapi32 
-lshell32 
-luser32 
-lkernel32 
-lmingw32 
-lgcc  
-lmoldname 
-lmingwex 
-lmsvcrt


LIBRARY_PATH=
-LC:MinGW32libgccmingw324.7.1 
-LC:mingw32libgcc 
-LC:mingw32libmingw32lib 
-LC:mingw32lib

OBJECT_FILES=
C:MinGW32libcrt2.o 
C:MinGW32libgccmingw324.7.1crtbegin.o

COLLECT2=C:MinGW32libexecgccmingw324.7.1collect2.exe

normal:
    $(CC) -c test.cpp
    $(COLLECT2) -Bdynamic $(OBJECT_FILES)  test.o -B$(type) -lstdc++ -Bdynamic  $(DEFAULT_FLAGS) $(LIBRARY_PATH) -o test.exe

optimized:
    $(CC) -c -O test.cpp
    $(COLLECT2) -Bdynamic $(OBJECT_FILES)  test.o -B$(type) -lstdc++ -Bdynamic  $(DEFAULT_FLAGS) $(LIBRARY_PATH) -o test.exe

smallest:
    $(CC) -c -O test.cpp
    $(COLLECT2) -Bdynamic $(OBJECT_FILES)  test.o -B$(type) -lstdc++ -Bdynamic  $(OPTIMAL_FLAGS) $(LIBRARY_PATH) -o test.exe

ultimate:
    $(CC) -c -O test.cpp
    $(COLLECT2) -Bdynamic $(OBJECT_FILES)  test.o -B$(type) -lstdc++ -Bdynamic  $(OPTIMAL_FLAGS) $(LIBRARY_PATH) -o test.exe
    strip test.exe
    upx test.exe

CLEAN:
    del *.exe *.o

Results(YMMV):

// Not stripped or compressed in any way
make normal    type=static     SIZE: 934KB
make normal    type=dynamic    SIZE: 64.0KB

make optimized type=dynamic    SIZE: 30.5KB
make optimized type=static     SIZE: 934KB

make smallest  type=static     (Linker Errors due to left out libraries)
make smallest  type=dynamic    SIZE: 25.6KB 

// Stripped and UPXed
make ultimate type=dynamic    (UPXed from 9728 bytes to 5120 bytes - 52.63%)
make ultimate type=static     (Linker Errors due to left out libraries)

A possible reason for the inclusion of -Bstatic in the default build options
is for better performance. I tried building astyle with -Bdynamic and got
a speed decrease of 1 second on average, even though the application was way
smaller than the original(400KB vs 93KB when UPXed).