C Programming about choosing my version of a function

Question

In function main() {...}

1) #include header file string.h

2) I prototype my own file, call it strcpy:

**char *strcpy(char *strSource , const char *dest);**

3) I also wish to use the "real" strlen function in string.h in main().

4) In another compilation file I have my version of strcpy.

Question: How can I get the linker to choose my version of strcpy instead of the prototype in string.h?

enter code here
#include <conio.h>
#include <string.h>
char *strcpy(char *source , const char *dest); 
void main()
{
char *s, *d;
strcpy(s,d);
getch();
}

#include <stdio.h>
char *strcpy(char *strDestination, const char *strSource)
{
char *ptr;
printf("made it!");
return ptr;
}

The title and tag don't suggest the same language. Please change it. — Mahesh, May 29 '12 at 20:10
Can I ask why you want to do this? Seems a little nefarious. :P I mean why not just name your strcpy something different, i.e. `myStrcpy();` — gbtimmon, May 29 '12 at 20:10
Namespace issues aside... `const char *` means a pointer to chars that you cannot change. Why would your `dest` be a `const char*`?? — HostileFork says dont trust SE, May 29 '12 at 20:55
The linker cares nothing about the declaration! Headers are not libraries. Libraries are not headers. — William Pursell, May 29 '12 at 20:56
@HostileFork: He used the [wrong order](http://www.cplusplus.com/reference/clibrary/cstring/strcpy/) of arguments, should be `char * strcpy ( char * destination, const char * source );`. — Zeta, May 29 '12 at 20:57
@gbtimmon - Wonderful suggestion. However, I am trying to understand the way C works. — Robert Massagli, May 29 '12 at 21:02

score 4 · Accepted Answer · answered May 29 '12 at 20:52

4

You can't do that in C. That's one of the reasons why C++ introduces namespaces.

The only thing you can do is use a non-conflicting name for your own functions.

answered May 29 '12 at 20:52

user703016

37,307
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Thanks. Using non-conflicting names is obvious, but are you sure "you can't do that in C"? My question is not whether it is standard, the question is: can it be done. – Robert Massagli May 29 '12 at 21:16
1

[You can abuse the preprocessor to use namespaces](http://stackoverflow.com/questions/389827/namespaces-in-c), but it's ugly. – user703016 May 29 '12 at 21:18
rather not use namespaces because it's not pure C. – Robert Massagli May 29 '12 at 21:21

score 1 · Answer 2 · answered May 29 '12 at 20:54

This is not a standard thing to do, and I'm pretty sure that if you can do it at all, you will have to read the manual for your linker. And if you try to port this, you will need to read the manual for each linker for each platform to which you try to port this.

The more usual way to do things is to write your own functions with your own names. If you need to hook functionality in a standard library, you would get the source for that library and build your own version.

Thanks for the comment and suggestion. No, I don't want to get into that much work! — Robert Massagli, May 29 '12 at 21:33

C Programming about choosing my version of a function

2 Answers2