Multi-file C Programs
• Large C programs spread across many C files
e.g. Linux operating system has 50,000+ .c files.
• Files provide a de facto module system in C.
• C functions can be called from any file, unless static Declaring functions static
avoids name clashes in huge programs
makes programs more readable/maintainable
• No checking of function parameters &return types between files
• By convention include .h files used to share information between .c files ensure types match between files.
Include Files
• Include .h files contain: function prototypes
type definitions #define’s
• .h files should not contain code (function definitions)
• #include with “” used to incorporate .h file put #include at top of .c file
Example: Include File
answer.h
int answer(double x); answer.c
#include “answer.h” int answer(double x) {
return x * 21; }
main.c
#include “answer.h”
int main(void) {
printf(“answer(2) = %d\n”, answer(1)); return 0;
}
Multi-file Compilation
$ dcc main.c answer.c -o answer
$ ./answer
42
Can also compile file separately creating bf .o files which contain machine code for one file.
$ dcc -c main.c
$ dcc -c answer.c
$ dcc main.o answer.o -o answer
$ ./answer
42
Useful with huge programs because faster to re-compile only part changed since last compilation.