how to convert string constant to preprocessing token in C

Question

I want to convert string constant to preprocessing token using macro. Example:

    // get the first character of marco argument to postfix of new data type.
    #define TYPE(typename) Prefix ## typename #typename[0]
    void main()
    {
        TYPE(int) a, b, c; // Prefixinti a, b, c;
        TYPE(float) x, y, z; // Prefixfloatf x, y, z;
        a = 3;
    }

is it possible in C/C++?
p/s: sorry for my poor English.
edited

But that should be all you need as long as your constant doesn't contain commas. — Medinoc
– Medinoc, Commented May 16, 2013 at 8:09
I want to create user-defined data types using X macros. Example: In OpenGL. GLPoint3i, GLPoint3f : get the first character in data type (int ,float) to the postfix for my data types. — dangkhoasdc
– dangkhoasdc, Commented May 16, 2013 at 8:11

pmg · Accepted Answer · 2013-05-16 10:54:22Z

4

#define TYPE(first_letter, rest) Prefix ## first_letter ## rest ## first_letter

typedef int TYPE(i,nt);
typedef float TYPE(f,loat);

int main(void)
{
  TYPE(i,nt) a, b, c; // Prefixinti a, b, c;
  TYPE(f,loat) x, y, z; // Prefixfloatf x, y, z;
}

edited May 16, 2013 at 10:54

answered May 16, 2013 at 9:38

pmg

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2 Comments

dangkhoasdc Over a year ago

Do you have a better solution? I want TYPE(int) a, b, c;// Prefixiniti a, b, c;

pmg Over a year ago

No, I don't know of another solution.

hetepeperfan · Accepted Answer · 2013-05-16 08:56:49Z

2

You should alway remeber what the preprocessor does, it modifies your source code before the compiler even sees it.

This does compile( I removed the quotes around int) , but is not so usefull:

#define TYPE(typename) typename

void main()
{
    TYPE(int) a, b, c;
    a = 3;
}

What you are doing results in the following code sent to the compiler:

TYPE("int") a, b, c;

results in"

"int" a, b, c;

where a string constant is followed by a couple of undeclared identifiers, which result in a syntax error

answered May 16, 2013 at 8:56

hetepeperfan

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2 Comments

dangkhoasdc Over a year ago

I want to create user-defined data types using X macros. Example: In OpenGL. GLPoint3i, GLPoint3f : get the first character in data type (int ,float) to the postfix for my data types.

hetepeperfan Over a year ago

I think the openGL variables are created using typedef. have a look at en.wikipedia.org/wiki/X_Macro here you can see how to use X macro,

CoffeeTableEspresso · Accepted Answer · 2020-04-23 22:33:59Z

2

It's not possible, even with templates in C++. By the way, avoid using typename in C-code as it's a keyword in C++ so your C code would be difficult to port.

Also void main() is not strictly portable; use int main() instead.

edited Apr 23, 2020 at 22:33

CoffeeTableEspresso

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answered May 16, 2013 at 8:13

Bathsheba

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2 Comments

Qaz Over a year ago

typename makes no difference since the preprocessor runs before the compiler.

Bathsheba Over a year ago

True but still naughty don't you think?

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