Calling of C functions with undefined number of parameters

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Note this question does not refer to ellipsis.

Consider the following code

#include <stdio.h>

void foo() {
    printf("I AM AWESOME\n");
}

main(void) {
    foo(1,2,3);
    foo();
return 0;
}

This program runs perfectly and provides the output. However, in case of 'main', this works irrespective of

main(void)

or

main()

When, defining foo as

foo(void)

gives an error - "too many arguments".

If both are functions, shouldn't they also follow the same rules?

When you declare a function without parameters it means to disable type checking and to use K&R calling convention. It does not mean that the function does not have parameters.

In ANSI when you want to explicitly say that the function does not have parameters, you need to declare it as fun(void).

Function with unknown number of parameters in C, Yes you can do it in C using what are referred to as Variadic Functions. The standard printf() and scanf() functions do this, for example. Put the� Rather than the standard function calling by taping the function name with arguments, we call only the pointer function by passing the number 3 as arguments, and that's it! Keep in mind that the function name points to the beginning address of the executable code like an array name which points to its first element.

the foo(void) takes no arguments(!!!), whereas foo() takes an unspecified number of arguments!

C - Variable Arguments, C - Variable Arguments - Sometimes, you may come across a situation, when you a function, which can take variable number of arguments, i.e., parameters, It should be noted that the function average() has been called twice and each� Prerequisite : Functions in C/C++ A function in C can be called either with arguments or without arguments. These function may or may not return values to the calling functions. All C functions can be called either with arguments or without arguments in a C program. Also, they may or may not return any values.

the is also somethg else in C called variable number of arguments

 void foo(int x, ...)

https://www.geeksforgeeks.org/variable-length-argument-c/

Calls with a Variable Number of Arguments, To call a function with a variable number of arguments, simply specify any An example is the printf function from the C run-time library. The C programming language provides a solution for this situation and you are allowed to define a function which can accept variable number of parameters based on your requirement. The following example shows the definition of such a function. int func(int, ) { . . . } int main() { func(1, 2, 3); func(1, 2, 3, 4); }

EXP37-C. Call functions with the correct number and , Do not call a function with the wrong number or type of arguments. The C Standard identifies five distinct situations in which undefined behavior (UB) may arise� Call External C Function Call a C function foo (u) from a MATLAB function from which you intend to generate C code. Create a C header file foo.h for a function foo that takes two input parameters of type double and returns a value of type double. double foo (double in1, double in2);

In C language, I have a function that takes a variable number of , Most answers given here give reference to Variadic Functions (Calling Variadics) , however the use of these fixes the number of arguments at compile time. Calling the Function in C Programming. Nothing but calling the original function with a valid number of arguments and valid data type. For example, Add (2, 3) NOTE: User defined function name should exactly match with the calling function in C Programming. C Function Definition. It is the place where we are going to put all the logics

Functions should not be defined with a variable number of , Appropriate arguments should be passed to UNIX/POSIX functions. Code Smell Blocking functions should not be called inside critical sections. Code Smell� // Invalid void add(int a, int b = 3, int c, int d); // Invalid void add(int a, int b = 3, int c, int d = 4); // Valid void add(int a, int c, int b = 3, int d = 4); If we are defining the default arguments in the function definition instead of the function prototype, then the function must be defined before the function call.

Comments
  • It doesn't work "perfectly" since you should get a warning about a missing function signature for foo(). The short answer is that main is special and different rules apply to it.
  • Is there any reason you would want to use foo()? It will probably be removed in the next standard.
  • main() is Implementation defined behaviour, and implementations will normally accept it. You should never use it, though.
  • The standard only allows explicitly int main(void) and int main(int argc, char *argv[]). Anything different is asking for trouble. Compilers may allow different main signatures or not.
  • c++ is a different story. () is the same as (void) there.
  • That's what is my question, shouldn't main also take unspecified number of arguments? If not declared with void and no arguments, if declared with 'void'?
  • and, if that's the case, is 'foo() can be called with unspecified number of arguments', a bug or a feature?
  • Why you care of main function ? you don't call main with parameters, just calling foo(). It's irrespective of main as you've wrote because you didn't call it (the system calls it).
  • Doesn't the system call _Start which in turn calls main?
  • @kesarling You can call main(); inside your program at any moment, and it is legal. I don't know of any situation where this would be desired, though. Maybe you can try it and have fun :)
  • respected sir/ma'am,Please read the note given at the start of the question carefully