C linking stage generates no warning

Question

I have the following files:

main.c :

int f(void);  
int main(void)
{
    f();
    return 0;
}

f.c:

char *f = "linker";

GNUMakefile:

CC = gcc
CFLAGS = -Wall -g

all: main

main: main.o f.o

main.o: main.c
f.o: f.c

clean:
    rm -rf *.o main

When running the makefile I get no compilation warnings/errors. Why?

Answer 1

Because you lied to the compiler ... and it trusts you.

In main.c you told the compiler f is a function (declaration / prototype), but f is, in fact, a pointer to a (unmodifiable) character array of length 7 defined in f.c (definition).

Don't lie to the compiler.

Answer 2

You've told the compiler f is a function. It isn't but there's no obligation on implementations to record the type which would be needed to warn here. Gcc doesn't, some other implementations might.

The workaround is to put the declaration of f into a header and include that in each translation unit which will make the error obvious.