Can we call an undeclared function in C++?

　　Calling an undeclared function is poor style in C (See this) and illegal in C++. So is passing arguments to a function using a declaration that doesn’t list argument types:

　　If we save the below program in a .c file and compile it, it works without any error. But, if we save the same in a .cpp file, it doesn’t compile.

 1 #include <stdio.h>
 2
 3 void f(); /* Argument list is not mentioned */
 4
 5 int main()
 6 {
 7     f(2); /* Poor style in C, invalid in C++*/
 8     getchar();
 9     return 0;
10 }
11
12 void f(int x)
13 {
14     printf("%d", x);
15 }

　　'c' parameter checking is not done at declaration but in 'c++' parameter checking is done at declaration

　　

　　Source: http://www2.research.att.com/~bs/bs_faq.html#C-is-subset

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　　2013-11-27　　12:11:06