CODEWITHSUNDEEP
ccompilationstatic-libraries
user4789408
user4789408

Reputation: 1196

C how to use library with multiple header tree

I am not understanding how I should compile with gcc the following .c and library.

example:

Files: "commons.h" and "commons.c" (the .c defines function etc...)

Files: "level1.h" and "level1.c", level1.c includes "commons.h"

Files: "level2.h" and "level2.c", level2.c includes "commons.h" and "level1.h"

I tried this and got "undefined reference to x" (where x is a function inside level1):

gcc commons.c -c -o commons.o    (OK)
gcc level1.c -c -o level1.o      (OK)
gcc level2.c -o level2.o   (error, undefined reference to x)

I expect to have level2 to be execute, I will only execute this.

How should I compile? Which order? (an example with command line will help me understand)

Upvotes: 0

Views: 72

Answers (1)

walnut
walnut

Reputation: 22152

Your last line should also use the -c flag in order to compile level2.c to an object file level2.o.

Afterwards the object files should be linked to create an executable, which is done via

gcc common.o level1.o level2.o -o my_executable

Alternatively you can directly supply all the source files to gcc without the -c flag, in which case it will perform all of the compilation and linking steps at once:

gcc common.c level1.c level2.c -o my_executable

Your error is currently caused, because you are instructing gcc without the -c option to compile and link the source file level2.c alone, but of course it can not be linked alone as it is missing symbols from the other source files.

The fact that level2.c contains main does not change anything about this. main is handled like any other function, only that it has a special meaning in the final executable as entry point.

Upvotes: 2

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