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.
#include<stdio.h> void f(); /* Argument list is not mentioned */ int main(){ f(2); /* Poor style in C, invalid in C++*/ getchar(); return 0;} void f(int x){ printf("%d", x);} |
Source: http://www2.research.att.com/~bs/bs_faq.html#C-is-subset
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