C Makefile未定义引用错误

Question

I am having slight problems with using makefile in C. Ive been following a tutorial in a textbook, but it doesnt seem to want to work. I have three files, message_hider.c, encrypt.h and encrypt.c. When I create a makefile for these files it returns an error, but when I run each command individually it works just fine. Here are my files.

encrypt.c

#include "encrypt.h"

void encrypt(char *message) {
char c;
while (*message) {
*message = *message ^ 31;
message++;
}
}

message_hider.c

#include <stdio.h>
#include "encrypt.h"

int main() {
char msg[80];
while (fgets(msg, 80, stdin)) {
encrypt(msg);
printf("%s", msg);
}
}

encrypt.h

void encrypt(char *message);

Makefile

message_hider: message_hider.o encrypt.o
    gcc message_hider.o encrypt.o -o message_hider
message_hider.o: message_hider.c encrypt.h
    gcc -c message_hider.c
encrypt.o: encrypt.c encrypt.h
    gcc -c encrypt.c

Error message

$ make message_hider
cc   message_hider.o   -o message_hider
message_hider.o:message_hider.c:(.text+0x17): undefined reference to `encrypt'
message_hider.o:message_hider.c:(.text+0x17): relocation truncated to fit: R_X86_64_PC32       against undefined symbol `encrypt'
/usr/lib/gcc/x86_64-pc-cygwin/4.8.2/../../../../x86_64-pc-cygwin/bin/ld:     message_hider.o: bad reloc address 0x0 in section `.pdata'
/usr/lib/gcc/x86_64-pc-cygwin/4.8.2/../../../../x86_64-pc-cygwin/bin/ld: final link    failed: Invalid operation
collect2: error: ld returned 1 exit status
<builtin>: recipe for target 'message_hider' failed
make: *** [message_hider] Error 1

Answer 1

$ make message_hider
cc   message_hider.o   -o message_hider

That is not the rule you've specified in your makefile. First off, it appears to be using cc rather than gcc . Second, there's no mention of encrypt.o in there which is why your link is failing.

Try to explicitly use the makefile, such as with:

make -f Makefile message_hider

It may be that it's picking up a different makefile, one that either has different rules or one that simply relies on the default rules like .co .

---

And, based on your update that:

make -f Makefile message_hider

gives you:

$ make -f Makefile message_hider
make: Makefile: No such file or directory
make: *** No rule to make target 'Makefile'. Stop.

that's the error you get when Makefile does not actually exist.

So you need to check that it's in the current directory, and named exactly as you expect.

That would explain the use of default rules as mentioned earlier, since your makefile isn't actually being picked up.

Another thing to check, though it's probably moot now that we've seen the error above, is that you're actually running the correct make program. Use which make to find out where it is (should be /usr/bin/make on CygWin) and make --version to check the version.