Programming in C

334 Chapter 15 Working with Larger Programs

If you’re working with a windows-based project management tool, such as

Metrowerks’ CodeWarrior, Microsoft Visual Studio, or Apple’s Xcode, then working with

multiple source files is easy.You simply have to identify the particular files that belong to

the project on which you are working, and the software handles the rest for you.The

next section describes how to work with multiple files if you’re not using such a tool,

also known as an Integrated Development Environment (IDE).That is, the next section

assumes you are compiling programs from the command line by directly issuing gccor

cccommands, for example.

Compiling Multiple Source Files from the Command Line

Suppose you have conceptually divided your program into three modules and have

entered the statements for the first module into a file called mod1.c, the statements for

the second module into a file called mod2.c, and the statements for your mainroutine

into the file main.c.To tell the system that these three modules actually belong to the

same program, you simply include the names of all three files when you enter the com-

mand to compile the program. For example, using gcc, the command

$ gcc mod1.c mod2.c main.c –o dbtest

has the effect of separately compiling the code contained in mod1.c,mod2.c, and

main.c.Errors discovered in mod1.c,mod2.c, and main.care separately identified by the

compiler. For example, if the gcccompiler gives output that looks like this:

mod2.c:10: mod2.c: In function 'foo':

mod2.c:10: error: 'i' undeclared (first use in this function)

mod2.c:10: error: (Each undeclared identifier is reported only once

mod2.c:10: error: for each function it appears in.)

then the compiler indicates that mod2.chas an error at line 10, which is in the function

foo. Because no messages are displayed for mod1.cand main.c, no errors are found

compiling those modules.

Typically, if there are errors discovered in a module, you have to edit the module to

correct the mistakes.^1 In this case, because an error was discovered only inside mod2.c,

you have to edit only this file to fix the mistake.You can then tell the C compiler to

recompile your modules after the correction has been made:

$ gcc mod1.c mod2.c main.c –o dbtest

$

Because no error message was reported, the executable was placed in the file dbtest.

Normally, the compiler generates intermediate object files for each source file that it

compiles.The compiler places the resulting object code from compiling mod.cinto the

file mod.oby default. (Most Windows compilers work similarly, only they might place

1.The error might be due to a problem with a header file included by that module, for example,

which means the header file and not the module would have to be edited.