CODEWITHSUNDEEP
ccompilationmakefile
Marty Wallace
Marty Wallace

Reputation: 35734

Make - Nothing to be done for - only with file extension

I have a simple c program - hello_world.c

As you can tell by the file name i am very very new to c.

I would expect to do the following to compile:

make hello_world.c

But this gives an error message: make: Nothing to be done for hello_world.c.

If i just do make hello_world it works i.e. without the extension.

Can someone explain why this is?

Upvotes: 5

Views: 7640

Answers (2)

Carl Norum
Carl Norum

Reputation: 224844

make takes a target as its argument. If you tell it you want to make hello_word.c, it will look, see that that file already exists and has no dependencies, and will decide it's up to date - hence nothing to do.

When you say make hello_world, make looks for hello_word, can't find it, then looks for hello_world.o, can't find it, then looks for hello_world.c, finds it, and then uses its implicit rule to build hello_world from it.

You can use make -d to see the decisions make is making along the way. Here's the example for make hello_world.c - I've trimmed out a bunch to showcase the last part, which is what you care about:

...
Considering target file `hello_world.c'.
 Looking for an implicit rule for `hello_world.c'.
 ...
 No implicit rule found for `hello_world.c'.
 Finished prerequisites of target file `hello_world.c'.
No need to remake target `hello_world.c'.
make: Nothing to be done for `hello_world.c'.

Then, for make hello_world:

...
Considering target file `hello_world'.
 File `hello_world' does not exist.
 Looking for an implicit rule for `hello_world'.
 Trying pattern rule with stem `hello_world'.
 Trying implicit prerequisite `hello_world.o'.
 Trying pattern rule with stem `hello_world'.
 Trying implicit prerequisite `hello_world.c'.
 Found an implicit rule for `hello_world'.
  Considering target file `hello_world.c'.
   Looking for an implicit rule for `hello_world.c'.
   Trying pattern rule with stem `hello_world'.
   ...
   No implicit rule found for `hello_world.c'.
   Finished prerequisites of target file `hello_world.c'.
  No need to remake target `hello_world.c'.
 Finished prerequisites of target file `hello_world'.
Must remake target `hello_world'.
cc     hello_world.c   -o hello_world
...
Successfully remade target file `hello_world'.

Upvotes: 10

danfuzz
danfuzz

Reputation: 4353

"Make" is a tool that is used to build non-trivial projects with multiple source files. If all you want to do is compile a single C file, use the C compiler. cc is usually available as the command-line name of the C compiler, though gcc is also a common name (which may refer to the same compiler).

Upvotes: -2

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