Try the error!

Don’t dispense with the ERROR.C file just yet. Don’t close the window, and don’t zap the project. (If you did, use your editor to load the ERROR.C file and prepare to reedit.)

Change Line 6 in the ERROR.C source code file to read this way:
retrun(0);

In case you don’t see it, the word return has been mangled to read retrun; the second r and the u are transposed. Otherwise, the zero in the parentheses and the semicolon are unchanged.

The way C works is that it just assumes that retrun is something you’re seri­ous about and not a typo. The compiler couldn’t care less. But the linker goes nuts over it. That’s because it’s the linker that glues program files together. It catches the error when it doesn’t find the word retrun in any of its libraries.

And, like any frazzled librarian, the linker spews forth an error message. Save the modified ERROR.C file to disk. Then recompile. Brace yourself for an error message along the lines of
temporary_filename.o: In function ‘main’:
temporary_filename.o: undefined reference to ‘retrun’

Or, the message may look like this:
temporary_filename.o(blah-blah):error.c: undefined reference to ‘retrun’

It’s harder to tell where the error took place here; unlike compiler errors, linker errors tend to be vague. In this case, the linker is explaining that the error is in reference to the word retrun. So, rather than use a line-number reference, you can always just search for the bogus text.

To fix the error, reedit the source code and change retrun back to return. Save. Recompile. The linker should be pleased.

As I mention elsewhere in this book, the GCC compiler both compiles and links.

If the linker is run as a separate program, it obviously produces its own error messages.

A temporary file is created by the compiler, an object code file that ends in .O — which you can see in the error message output. This object code file is deleted by GCC.

The linker’s job is to pull together different pieces of a program. If it spots something it doesn’t recognize, such as  , it assumes, “Hey,
maybe it’s something from another part of the program.” So the error slides by. But, when the linker tries to look for the unrecognized word, it hoists its error flags high in the full breeze.

 

See also:

The Four Steps to build a C program

5 steps to reedite your C source code file

What's the meaning of recompiling the C program?