gcc -o hello.e hello.c, compile hello.c, output the executable file hello.e

gcc -g hello.c, compile hello.c and generate debug information for gdb

gcc -O hello.c, compile hello.c and generate optimized executable program

• -O0, no optimization
• -O1, -O, late cycle test, default value
• -O2, production use
• -O3, generate optimized executable file

gcc -v hello.c, output the detailed information of compiling

gcc -Wall hello.c, generate more warning details

#include <stdio.h>

int main()
{
	printf("Hello World!\n");

	return 0;
}
		

// main.c
extern void disp();

int main()
{
	disp();

	return 0;
}
		

// util.c
#include <stdio.h>

void disp()
{
	printf("Hello World!\n");
}
		

gcc -c main.c, generate main.o

gcc -c util.c, generate util.o

gcc main.o util.o -o hello.e, generate hello.e

// util.h
#ifndef UTIL_H
#define UTIL_H

void disp();

#endif
		

// main.c
#include "util.h"

int main()
{
	disp();

	return 0;
}
		

// utill.c
#include <stdio.h>
#include "util.h"

void disp()
{
	printf("Hello World!\n");
}
		

1. gcc -c -fpic -I include src/util.c, generate util.o
2. gcc -shared -o lib/libhello.so util.o, generate dynamic library
3. gcc -o hello.e -I include src/main.c -L ./lib -lhello, compile main.c and link library
4. Making library available at run time
   • export LD_LIBRARY_PATH=$PWD/lib:$LD_LIBRARY_PATH, add "lib" folder to search directory
   • gcc -L ./lib -Wl,-rpath=$PWD/lib -Wall -o test -I include src/main.c -lhello, using rpath which is run time search path
   • cp lib/libhello.so /usr/lib, chmod 0755 /usr/lib/libhello.so, ldconfig
5. ./hello.e, run the program

include

• -I, specify search path for header files
• C_INCLUDE_PATH
• /usr/local/include, default directory of .h files

library

• -L, specify search path for libries
• LD_LIBRARY_PATH
• /lib, /usr/lib, default directory of .so, .lib, and .dll files

rpath

Options for Directory Search

Shared libraries with GCC on Linux

gcc commands