CODEWITHSUNDEEP
c++cgccname-mangling
Daniel Frużyński
Daniel Frużyński

Reputation: 2189

C++ name mangling in C

C language does not use name mangling like C++. This can lead to subtle bugs, when function prototype is declared differently in different files. Simple example:

/* file1.c */
int test(int x, int y)
{
    return y;
}

/* file2.c */
#include <stdio.h>

extern int test(int x);

int main()
{
    int n = test(2);
    printf("n = %d\n", n);
    return 0;
}

When compiling such code using C compiler (in my case gcc) no errors are reported. After switching to C++ compiler, linking will fail with error "undefined reference to 'test(int)'". Unfortunately in practice this is not so easy - there are cases when code is accepted by C compiler (with possible warning messages), but compilation fails when using C++ compiler.

This is of course bad coding practice - all function prototypes should be added to .h file, which is then included in files where function is implemented or used. Unfortunately in my app there are many cases like this, and fixing all of them is not possible in short term. Switching to g++ is also not at option, I got compilation error quite fast.

One of possible solutions would be to use C++ name mangling when compiling C code. Unfortunately gcc does not allow to do this - I did not found command line option to do this. Do you know if it is possible to do this (maybe use other compiler?). I also wonder if some static analysis tools are able to catch this.

Upvotes: 4

Views: 1429

Answers (2)

Freyja
Freyja

Reputation: 40804

Using splint catches these kinds of errors.

foo.c:

int test(int x);
int main() {
    test(0);
}

bar.c:

int test(int x, int y) {
    return y;
}

Running splint:

$ splint -weak foo.c bar.c
Splint 3.1.2 --- 20 Feb 2009

bar.c:1:5: Function test redeclared with 2 args, previously declared with 1
  Types are incompatible. (Use -type to inhibit warning)
   foo.c:4:5: Previous declaration of test

Finished checking --- 1 code warning

Upvotes: 1

ach
ach

Reputation: 2373

~/dev/temp$ cat > a.c
int f(int x, int y) { return x + y; }

~/dev/temp$ cat > b.c
extern int f(int x); int g(int x) { return f(x + x); }

~/dev/temp$ splint *.c
Splint 3.1.2 --- 03 May 2009

b.c:1:12: Function f redeclared with 1 arg, previously declared with 2
  Types are incompatible. (Use -type to inhibit warning)
   a.c:1:5: Previous declaration of f

Finished checking --- 1 code warning
~/dev/temp$

Upvotes: 0

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