#define usage in C/C++

Question

I need to write such a define in C/C++

#define scanf( fscanf(inf,

in order to replace each scanf( with fscanf(inf, literary

But I do not know how...

Thanks

Answer 1

You want to use a Variadic macro.

In your case, I believe you want:

#define scanf(...) fscanf(inf,__VA_ARGS__)

Answer 2

You can't replace a parenthesis. If you're using Visual C++, then you can use a variadic macro to accomplish what you want:

#define scanf( format, ... ) fscanf( inf, format, __VA_ARGS__ )

Other compilers may have a similar facility, but I'm not familiar with them.

Answer 3

not possible the way you tried of course.

you have to do things like

#define scanf(S, ...) fscanf(inf, S, __VA_ARGS__)

See e.g. here

EDIT: GNU cpp supports variadic macros too; it is VA_ARGS preceded by double underscore and ended with double underscore... I have to study escaping markup here...

Answer 4

Just write all your code using fscanf, and define the file name with a macro like this:

#ifdef USE_SCANF
#define SCANF_FILE(file) stdin
#else
#define SCANF_FILE(file) file
#endif

fscanf(SCANF_FILE(blah), "%d", &a);

Answer 5

I need to write such a define in C++

No, you don't. What you really want to do is redirect stdin.

freopen(inf, "r", stdin);