CODEWITHSUNDEEP
c++c
user1884325
user1884325

Reputation: 2550

Struct compiler problems in C

The following can be included from a .cpp file and the compiler won't complain about it.

typedef struct _SomeName {
    char NameID[MaxSize];  
    UserId notUsed;
    UserInstance instance;

    bool operator==(const struct _SomeName& rhs) const
    {
        return (strncmp(NameID, rhs.NameID, MaxSize) == 0);
    }
    bool operator!=(const struct _SomeName& rhs) const { return !(*this == rhs); };
} SomeName;

How do I rewrite the above so that it's possible to include it from a .c file ?

Upvotes: 0

Views: 145

Answers (3)

M.M
M.M

Reputation: 141544

The other solutions posted so far have a problem that you cannot use it in a project which mixes C and C++. I am guessing from the context of your question that you might want to do that. If you try that, you may get silent undefined behaviour because the structure could have a different layout in different translation units.

I'd suggest this version:

typedef struct 
{
    char NameID[MaxSize];  
    UserId notUsed;
    UserInstance instance;    
} SomeName;

#ifdef __cplusplus
inline bool operator==( SomeName const &lhs, SomeName const &rhs )
{ 
     return strcmp(lhs.NameID, rhs.NameID) == 0;
}
inline bool operator!=( SomeName const &lhs, SomeName const &rhs )
{
     return !operator==( lhs, rhs );
}
#endif

Upvotes: 1

Steen
Steen

Reputation: 207

You cannot get the exact functionality of the c++ struct, but if you use the __cplusplus conditional, you can leave out the parts, the C compiler will not compile.

typedef struct _SomeName {
    char NameID[MaxSize];  
    UserId notUsed;
    UserInstance instance;

    #ifdef __cplusplus
    bool operator==(const struct _SomeName& rhs) const
    {
        return (strncmp(NameID, rhs.NameID, MaxSize) == 0);
    }
    bool operator!=(const struct _SomeName& rhs) const { return !(*this == rhs); };
    #endif
} SomeName;

If you need the equal and not equal operator, in both c and c++, I suggest you remove the operator definitions from the struct, and write a pure c interface implementing a SomeNameEquals and SomeNameNotEquals function.

Upvotes: 1

John Bollinger
John Bollinger

Reputation: 180058

Supposing that declarations of types UserId and UserInstance are in scope, you should be able to write this:

typedef struct _SomeName {
    char NameID[MaxSize];  
    UserId notUsed;
    UserInstance instance;
#ifdef __cplusplus
    bool operator==(const struct _SomeName& rhs) const
    {
        return (strncmp(NameID, rhs.NameID, MaxSize) == 0);
    }
    bool operator!=(const struct _SomeName& rhs) const { return !(*this == rhs); };
#endif
} SomeName;

Upvotes: 1

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