C++ reserved word as function pointer name in C struct

Question

I suspect I know the answer to this already, but am curious if any experts out there have any tricks.

I have a C library built with the intention of being a C framework (unsafe functions unused, similar naming convention cross-platform, etc.). This works fine, up until I try to use it within a C++ project, where the C 'namespaced' function name conflicts with a C++ reserved word, in this case delete.

Here's the 'file' namespace, where I want it delete to be one of the function names:

#include <stdio.h>

#if defined(__linux__) || defined(BSD)
#   include <fcntl.h>
#endif


#if defined(__cplusplus)
#   if defined(_MSC_VER)
#       pragma warning ( push )
        // Disable: default constructor could not be generated
#       pragma warning ( disable : 4510 )
        // Disable: assignment operator could not be generated
#       pragma warning ( disable : 4512 )
        // Disable: struct <unnamed-tag> can never be instantiated
#       pragma warning ( disable : 4610 )
#   endif
extern "C" {
#endif



typedef struct
{
    int(*const close)(FILE* fp);
    int(*const copy)(const char* src, const char* dest);
    int(*const delete)(const char* path);
    int(*const flush)(FILE* fp);
    long(*const get_file_size)(FILE* fp);
    long(*const get_size)(const char* path);
    FILE*(*const open)(const char* name, const char* modes);
    int(*const path_exists)(const char* path);
    size_t(*const read)(void* ptr, size_t size, size_t count, FILE* stream);
    size_t(*const write)(const void* ptr, size_t size, size_t count, FILE* stream);

} namespace_file;

extern namespace_file const file;



#if defined(__cplusplus)
}   // extern "C"
#   if defined(_MSC_VER)
#       pragma warning ( pop )
#   endif
#endif

Now I'm writing some tests using gtest, and encounter the reserved word issue - is there anyway to bypass this, or shall I simply rename the function to purge or similar?

TEST(cfwkFile, fDelete)
{
    // all three of these error as 'delete' is reserved
    EXPECT_EQ(0, file.delete(CFWK_TEST_FAIL_FILE));
    EXPECT_EQ(1, file.delete(CFWK_TEST_PASS_FILE));
    EXPECT_EQ(1, file.delete(CFWK_TEST_PASS_FILE_COPY));
}

Jural

You can't use C++ reserved words as identifiers in your C code if you intend to feed them to a C++ compiler. – Madeira

Why not just #define delete to something else before including the header and #undef delete afterwards? – Vanir

@R.. That's probably a very bad idea! Even with the #undef. – Archival

@R.. Technically you can't #define a keyword. Most compilers support it as an extension though. – Madeira

@TavianBarnes, You legally can if not using the standard library. Unfortunately, with third party headers, it might sometimes end up being the best option under the circumstances. – Pannier

@πάνταῥεῖ: If it's your own code and you intend to use it as a C++-accessible interface, then yes, I would agree. But if it's a third-party C library and you're using it as foreign-language code from C++, that might be the simplest solution. – Vanir

I'm trying to make this as standard as possible, since my intention is for others to be using it; defining keywords may not end too well, especially since a rename would just be a lot safer! – Jural

@R.. From N3242, §17.6.4.3.1, p. 2: "A translation unit shall not #define or #undef names lexically identical to keywords". Admittedly there seems to be some disagreement over what "keyword" means in that context but I always took it to mean that #define delete is illegal. – Madeira

@R.. Oh never mind, §17.6.4 "describes restrictions on C++ programs that use the facilities of the C++ standard library", so you're right. – Madeira

Answer 1

"is there anyway to bypass this, or shall I simply rename the function to purge or similar?"

  int(*const delete)(const char* path);
          // ^^^^^^

Yes you should rename it, if the code in question is under your control!
You simply can't use a function pointer named delete in C++ compiled code, because it's a reserved keyword for the language.

You just need to make it different from the keyword. Instead of renaming it to purge, which might be misleading from a semantic level, you can still use something like

int(*const delete_)(const char* path);
              // ^

to get it distinct from the C++ keyword.

---

About your comments mentioning kind of asymetric/inconsistent naming:
Just use a _ postfix for all of them. As giving an opiniion, that's my preferred style for member variables of structs or classes anyway.

Trishtrisha

Yeah, was wondering if anyone had any magic tricks to get round it, but wasn't getting my hopes up! Just wanted an 'expected' function name, 'delete' a file is significantly more common that 'purge' - hey ho! – Jural

@Jural You can still use something like delete_ to come over these semantic level concerns. – Archival

Good point, hadn't considered that; may look just a little more peculiar than the others, but that ticks all the checkboxes for expectations. Think I'll do that.. – Jural

what about remove ? – Sink

Or delet as homage to creat. :3 – Suspend

lol :P Might just be me, but remove/unlink just isn't as clear to the final result in comparison to delete... – Jural

@Jural "... may look just a little more peculiar than the others ..." Just use a _ postfix for all of them. That's my preferred style for any member variables of structs or classes anyway. – Archival

An idea, but I'd rather make it the exception than the rule - I'm careful enough for naming schemes for everything else, it's just purely the semantics of this individual case :) – Jural