Using a DEFINITION in a scanf in C (type specifier)

Question

So my original code was:

scanf("%20s %20s", Player1.name, Player2.name);

If I want to make my code more flexible can I do, or is there a similar way to do:

.#define MAX_NAME_IN 20
...
scanf("%MAX_NAME_INs %MAX_NAME_INs", Player1.name, Player2.name);
...

Can you give us example what you would like to read... then answers would be better — Digital_Reality, Jan 21 '14 at 15:38
Have you seen this: [Can I use scanf to capture a directive with a width specified by a variable?](http://stackoverflow.com/q/1549906/758831)? — wmorrison365, Jan 21 '14 at 15:39
For a Microsoft-only solution, you can used `scanf_s`, as in http://stackoverflow.com/q/18836661/318716 — Joseph Quinsey, Jan 24 '14 at 17:00

BLUEPIXY · Accepted Answer · 2014-01-21T16:00:58.403

2

#define MAX_NAME_IN 20
#define S_(x) #x
#define S(x) S_(x)
...
scanf("%" S(MAX_NAME_IN) "s %" S(MAX_NAME_IN) "s", Player1.name, Player2.name);

replace by preprocessor like this

S(MAX_NAME_IN) => S_(20) => "20"

scanf("%" S(MAX_NAME_IN) "s %" S(MAX_NAME_IN) "s", Player1.name, Player2.name);
↓
scanf("%" "20" "s %" "20" "s", Player1.name, Player2.name);

and "%" "20" "s %" "20" "s" is interpreted as "%20s %20s" by compiler.

edited Jan 21 '14 at 16:00

answered Jan 21 '14 at 15:46

BLUEPIXY

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oh awesome, can you please explain how this works? – Theo Jan 21 '14 at 15:54
why could you not have done #define MAX_NAME_IN 20 #define S(x) #x? – Theo Jan 21 '14 at 16:08
@Theo your case is converted as follows: `S(MAX_NAME_IN)` => `"MAX_NAME_IN"` – BLUEPIXY Jan 21 '14 at 16:23

Using a DEFINITION in a scanf in C (type specifier)

1 Answers1