What is going on!!!!

client.c

#include <stdio.h>

#ifdef HEADER
#include "lib.h"
#endif

int main(int argc, char* argv[]) {
  float a = 5.0;
  int b = 10;
  double c = 2.0;

  printf("in main, float  a = %f\n", a);
  printf("in main, int    b = %d\n", b);
  printf("in main, double c = %f\n", c);

  printf("Calling functions...\n");

  g_float(a);
  g_int(b);
  g_double(c);
  
  return 1;
}

lib.c

#include <stdio.h>
#include "lib.h"

void g_float(float a) {
  printf("In g_float, you passed a = %f\n", a);
}

void g_int(int b) {
  printf("In g_int, you passed b = %d\n", b);
}

void g_double(double c) {
  printf("In g_double, you passed c = %f\n", c);
}

lib.h

#ifndef LIB_H
#define LIB_H

void g_float(float a);
void g_int(int b);
void g_double(double c);

#endif

Makefile

all:
	gcc -DHEADER client.c lib.c -o withheader
	gcc          client.c lib.c -o withoutheader

stdout

rmcgibbo@Roberts-MacBook-Pro-2 ~/local/mdtraj/ctest
$ gcc --v
Using built-in specs.
Target: i686-apple-darwin11
Configured with: /private/var/tmp/llvmgcc42/llvmgcc42-2335.15~25/src/configure --disable-checking --enable-werror --prefix=/Developer/usr/llvm-gcc-4.2 --mandir=/share/man --enable-languages=c,objc,c++,obj-c++ --program-prefix=llvm- --program-transform-name=/^[cg][^.-]*$/s/$/-4.2/ --with-slibdir=/usr/lib --build=i686-apple-darwin11 --enable-llvm=/private/var/tmp/llvmgcc42/llvmgcc42-2335.15~25/dst-llvmCore/Developer/usr/local --program-prefix=i686-apple-darwin11- --host=x86_64-apple-darwin11 --target=i686-apple-darwin11 --with-gxx-include-dir=/usr/include/c++/4.2.1
Thread model: posix
gcc version 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2335.15.00)

rmcgibbo@Roberts-MacBook-Pro-2 ~/local/mdtraj/ctest
$ make
gcc -DHEADER client.c lib.c -o withheader
gcc          client.c lib.c -o withoutheader

rmcgibbo@Roberts-MacBook-Pro-2 ~/local/mdtraj/ctest
$ ./withheader 
in main, float  a = 5.000000
in main, int    b = 10
in main, double c = 2.000000
Calling functions...
In g_float, you passed a = 5.000000
In g_int, you passed b = 10
In g_double, you passed c = 2.000000

rmcgibbo@Roberts-MacBook-Pro-2 ~/local/mdtraj/ctest
$ ./withoutheader 
in main, float  a = 5.000000
in main, int    b = 10
in main, double c = 2.000000
Calling functions...
In g_float, you passed a = 0.000000
In g_int, you passed b = 10
In g_double, you passed c = 2.000000

Take a look at line 20 vs line 30 in the stdout file.

WHAT IS HAPPENING?

it's not really that crazy, but it's still annoying.

http://stackoverflow.com/questions/6244048/strange-behavior-of-float-in-function-definition-and-declaration-definition-mis