Following is the very minimum syntax required for the “C” program, we can call it as the first C program which we can write.
vim minimum-c-program.c
main() {
}
That is, the most minimum syntax required for a simple C program should contain 3 important things as,
1. main function which is the entry point of the C program
2. open & close bracket () after main
3. open & close curly brace {}
Now, Lets try to compile this program as,
$ gcc -o minimum-c-program_exe minimum-c-program.c
Execute the binary executable created using above command as,
./minimum-c-program_exe
Now, we can check code & data size of this program as,
$ size minimum-c-program_exe text data bss dec hex filename 1017 272 4 1293 50d minimum-c-program
$ nm -S minimum-c-program
0804a018 B __bss_start
0804a018 00000001 b completed.7200
0804a010 D __data_start
0804a010 W data_start
08048320 t deregister_tm_clones
08048390 t __do_global_dtors_aux
08049f0c t __do_global_dtors_aux_fini_array_entry
0804a014 D __dso_handle
08049f14 d _DYNAMIC
0804a018 D _edata
0804a01c B _end
08048454 T _fini
08048468 00000004 R _fp_hw
080483b0 t frame_dummy
08049f08 t __frame_dummy_init_array_entry
08048558 r __FRAME_END__
0804a000 d _GLOBAL_OFFSET_TABLE_
w __gmon_start__
08048470 r __GNU_EH_FRAME_HDR
0804828c T _init
08049f0c t __init_array_end
08049f08 t __init_array_start
0804846c 00000004 R _IO_stdin_used
w _ITM_deregisterTMCloneTable
w _ITM_registerTMCloneTable
08049f10 d __JCR_END__
08049f10 d __JCR_LIST__
w _Jv_RegisterClasses
08048450 00000002 T __libc_csu_fini
080483f0 0000005d T __libc_csu_init
U [email protected]@GLIBC_2.0
080483db 0000000a T main
08048350 t register_tm_clones
080482e0 T _start
0804a018 D __TMC_END__
08048310 00000004 T __x86.get_pc_thunk.bx
You can check which libraries this program uses using following command,
$ ldd minimum-c-program_exe linux-gate.so.1 => (0xb7722000) libc.so.6 => /lib/i386-linux-gnu/libc.so.6 (0xb753d000) /lib/ld-linux.so.2 (0x80038000)
The other important commands you can try to udnerstand are as bellow,
$ objdump -Dxls minimum-c-program_exe
$ readelf -a minimum-c-program_exe
In the next post, we will try to understand how this program executes in run time as “Understanding execution of very minimal C program in Linux / Ubuntu”