No previous prototype?
In C, this:
void printBind();
is not a prototype. It declares a function that returns nothing (void
) but takes an indeterminate list of arguments. (However, that list of arguments is not variable; all functions taking a variable length argument list must have a full prototype in scope to avoid undefined behaviour.)
void printBind(void);
That's a prototype for the function that takes no arguments.
The rules in C++ are different - the first declares a function with no arguments and is equivalent to the second.
The reason for the difference is historical (read 'dates back to the mid-1980s'). When prototypes were introduced into C (some years after they were added to C++), there was an enormous legacy of code that declared functions with no argument list (because that wasn't an option before prototypes were added), so backwards compatibility considerations meant that SomeType *SomeFunction();
had to continue meaning 'a function that returns a SomeType *
but for which we know nothing about the argument list'. C++ eventually added the SomeType *SomeFunction(void);
notation for compatibility with C, but didn't need it since type-safe linkage was added early and all functions needed a prototype in scope before they were defined or used.
Stas Jaro
C++, C, Objective-C, VHDL, Java, AVR Assembly, HTML, Javascript, PHP
Updated on August 11, 2022Comments
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Stas Jaro almost 2 years
Possible Duplicate:
Error: No previous prototype for function. Why am I getting this error?I have a function that I prototyped in the header file, however Xcode still gives me warning
No previous prototype for the function 'printBind'
. I have the functionsetBind
prototyped in the same way but I do not get an warning for this function in my implementation.CelGL.h
#ifndef Under_Siege_CelGL_h #define Under_Siege_CelGL_h void setBind(int input); void printBind(); #endif
CelGL.c
#include <stdio.h> #include "CelGL.h" int bind; void setBind(int bindin) { // No warning here? bind = bindin; } void printBind() { // Warning here printf("%i", bind); }
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sherrellbc over 6 yearsThough I now understand the reason for the error, I do not really understand the usefulness of this feature. When would you define a function with an indeterminate parameter list and what exactly does this have to do with C++? Is this a useful feature in C++?
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Jonathan Leffler over 6 yearsYou can’t define a prototype with an indeterminate argument list in C++. In C++, that means “no arguments”, not “indeterminate arguments”. The feature is not so much useful as a necessary concession to reality. When C was standardized, the entire vast code base was written without prototypes; they hadn’t existed in C. The empty parenthesis notation was all there was in pre-standard C. To have outlawed it would have killed the nascent C standard. That was still true for C99. It was less clear for C11, but was left unchanged.