What is a symbol in programmation as referred in ar command

Question

I see this term a lot, 'symbol', and after searching on google I still can't find a definition that makes sense to me.

For example in the manual of ar command on Linux, it's said :

ar creates an index to the symbols defined in relocatable object modules in the archive when you specify the modifier s.

Are function declarations / variable declarations / defines / structure declarations etc, symbols ? Or is a symbol a term for .o files ?

In this context, what is a symbol exactly ? Act like I'm a complete beginner who knows nothing when you form your answer please !

Answer 1

A symbol is the name of things (functions, variables etc). Here is an example file:

#include <stdlib.h>

struct foo {
    char *a;
};
struct foo global_foo;
static struct foo static_foo;

struct foo *foo_create() {
     return malloc(sizeof(struct foo));
}

which I then compile and make an archive and then use nm to list its symbols:

$ gcc -c 1.c && ar -rc 1.a 1.o && nm -s 1.a

Archive index:
global_foo in 1.o
foo_create in 1.o

1.o:
0000000000000000 T foo_create
0000000000000000 B global_foo
                 U _GLOBAL_OFFSET_TABLE_
                 U malloc
0000000000000008 b static_foo