Linux Libraries

Linux Libraries comes in two forms: Static and shared.

Static Libraries

Static libraries link needed code from the object (.o) files or an archive of object files into the binary file.

Static example

Pack two files file1.c and file2.c to libfilearchive.a

File1.c

//Author: Henrik Thomsen <heth@mercantec.dk>
//Name: file1.c
#include <stdio.h>
#define MB 1024*1024
void p1( void ) {
        // Initialize 1MB array first and last member
        // so we are sure the array is not truncated.
        const char txt[MB];// = {[0]=0x0ff, [MB-1]=0xff };
        printf("I am file1\n");
        printf("txt is %d bytes\n", sizeof(txt) );
}

File2.c

//Author: Henrik Thomsen <heth@mercantec.dk>
//Name: file2.c
#include <stdio.h>
void p2( void ) {
        printf("I am file2\n");
}

Creating libfilearchive.a

[heth@localhost ]$ gcc -c file1.c
[heth@localhost ]$ gcc -c file2.c
[heth@localhost ]$ ar rc libfilearchive.a file1.o file2.o
[heth@localhost ]$ ls -l
-rw-rw-r--. 1 heth heth         334 Dec 23 10:32 file1.c
-rw-rw-r--. 1 heth heth 1050248 Dec 23 10:32 file1.o
-rw-rw-r--. 1 heth heth         125 Dec 23 10:26 file2.c
-rw-rw-r--. 1 heth heth       1496 Dec 23 10:31 file2.o
-rw-rw-r--. 1 heth heth 1051950 Dec 23 10:32 libfilearchive.a

Notice the size of the object file from file1.c and the .a archivefile. It contains the 1MB const array.

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