Should I worry about gcc -pedantic option now?

Question

I have just started to learn C as a hobby. I am doing it with the "C programming: A Modern Approach" book. There is a first program there which is called pun.c. Here is the code:

#include <stdio.h>

int main(void)
{
  int int_figure;
  float float_figure;

  int_figure = 12;
  float_figure = 12.0;
  printf("To C or not to C, this is a question\n");
  printf("%d\n", int_figure);
  printf("%.2f\n", float_figure);
  return 0;
}

Actually it does not matter because the thing I want to ask about is the same with any .c file compilation with gcc.

So in the book there are some options for gcc which allow finding errors during compilation.One of them is -Wall, another one is -pedantic. So when I compile the file with this option, the output in terminal is the following:

nickdudaev|c $ gcc -o -Wall pun pun.c
pun: In function `_fini':
(.fini+0x0): multiple definition of `_fini'
/usr/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../lib/crti.o:(.fini+0x0): first defined here
pun: In function `data_start':
(.data+0x0): multiple definition of `__data_start'
/usr/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../lib/crt1.o:(.data+0x0): first defined here
pun: In function `data_start':
(.data+0x8): multiple definition of `__dso_handle'
/usr/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/crtbegin.o:(.data+0x0): first defined here
pun:(.rodata+0x0): multiple definition of `_IO_stdin_used'
/usr/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../lib/crt1.o:(.rodata.cst4+0x0): first defined here
pun: In function `_start':
(.text+0x0): multiple definition of `_start'
/usr/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../lib/crt1.o:(.text+0x0): first defined here
pun: In function `_init':
(.init+0x0): multiple definition of `_init'
/usr/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../lib/crti.o:(.init+0x0): first defined here
/tmp/cc2TRR93.o: In function `main':
pun.c:(.text+0x0): multiple definition of `main'
pun:(.text+0xf6): first defined here
/usr/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/crtend.o:(.tm_clone_table+0x0): multiple definition of `__TMC_END__'
pun:(.data+0x10): first defined here
/usr/bin/ld: error in pun(.eh_frame); no .eh_frame_hdr table will be created.
collect2: error: ld returned 1 exit status

The program although runs correctly.

nickdudaev|c $ ./pun
To C or not to C, this is a question
12
12.00

So to the questions.

1. Should I on this stage (of learning) worry about this output and at all use those options?
2. Do I have probably some systematic error? Because output is the same for any file compilation. Maybe something is not properly installed?

I tried to search Google, but the only thing I found is descriptions of what gcc options do. But nothing about possible output and what to do with it.

Answer 1

This:

gcc -o -Wall pun pun.c

doesn't look right. You're saying -Wall where you should say the name of the output, i.e. the argument to -o.

Try:

gcc -Wall -o pun pun.c

Basically you're feeding pun, the old binary, to gcc as a source file.

Answer 2

The -o option in gcc is used to specify a custom output file name, otherwise,

If -o is not specified, the default is to put an executable file in a.out.

The recommended format is -o file. The next expected argument after -o is a filename, not another switch. See the online manual for more details.

You should re-write your compilation statement as

gcc -o pun pun.c -Wall