Header Files and Libraries

• Many of C's facilities are provided via library functions such as scanf
  
  
• To produce an executable:
  • #include header files in code to be compiled;
  • link in (previously compiled) libraries;

Compilation and Header Files

• #include <stdio.h>
  
  
• #include "path/my_defs.h"

Linking and Libraries

• Executable code corresponding to stdio.h (and more) is to be found in libc.a;
  
  
• executable code corresponding to other header files is found in other libraries.

Example

Compile and link:

#include <stdio.h> #include <math.h> main() { int i; float x; for (i = 0; i <= 10; i++) { x = sin(i); printf("i = %d, ", i); printf("x = %f\n", x); } }

• Use

  gcc -lm -o maths maths.c

  to link in libm.a

Search Path Considerations

Each system will have default search paths on which the compiler and linker will search for header files and precompiled libraries. Sometimes we need to add to the default paths. For example:

gcc -I/home/simonh/my_h -L/home/simonh/my_libs -lmylib my_prog.c