function-declaration | 易学教程

Why do functions need to be declared before they are used?

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When reading through some answers to this question , I started wondering why the compiler actually does need to know about a function when it first encounters it. Wouldn't it be simple to just add an extra pass when parsing a compilation unit that collects all symbols declared within, so that the order in which they are declared and used does not matter anymore? One could argue, that declaring functions before they are used certainly is good style, but I am wondering, is there are any other reason why this is mandatory in C++? Edit - An example to illustrate: Suppose you have to functions that

Function without return type specified in C

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问题 I came across this piece of code in C: #include <stdio.h> main( ) { int i = 5; workover(i); printf("%d",i); } workover(i) int i; { i = i*i; return(i); } I want to know how the declaration of the function "workover" is valid? What happens when we don't mention the return type of a function? (can we return anything?).The parameter is also just a variable name, how does this work? 回答1: If you do not specify a return type or parameter type, C will implicitly declare it as int . This is a "feature

Can a function prototype typedef be used in function definitions?

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问题 I have a series of functions with the same prototype, say int func1(int a, int b) { // ... } int func2(int a, int b) { // ... } // ... Now, I want to simplify their definition and declaration. Of course I could use a macro like that: #define SP_FUNC(name) int name(int a, int b) But I'd like to keep it in C, so I tried to use the storage specifier typedef for this: typedef int SpFunc(int a, int b); This seems to work fine for the declaration: SpFunc func1; // compiles but not for the

Why can’t I assign values to a variable inside a named function expression with the same name?

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问题 This is a named function expression with the name test . Inside, I assign 123 to a variable, also named test . Then test is logged. The function prints its body in the console, but not 123 . What is the reason for such behavior? (function test() { test = 123; console.log( test ); }()); Where does my explanation of function execution fail? Start of function execution: test is a local variable that references the function itself Local variable test is reassigned to number 123 console.log(test)

Function declaration in CoffeeScript

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问题 I notice that in CoffeeScript, if I define a function using: a = (c) -> c=1 I can only get the function expression : var a; a = function(c) { return c = 1; }; But, personally I often use function declaration ,for example: function a(c) { return c = 1; } I do use the first form, but I'm wondering if there is a way in CoffeeScript generating a function declaration. If there is no such way, I would like to know why CoffeeScript avoid doing this. I don't think JSLint would holler an error for

Maximum number of parameters in function declaration

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问题 I know that minimum number of parameters in function definition is zero, but what is the maximum number of parameters in function definition? I am asking the question just for the sake of knowledge and out of curiosity, not that I am going to write a real function. 回答1: Yes, there are limits imposed by the implementation. Your answer is given in the bold text in the following excerpt from the C++ Standard. 1. C++ Language Annex B - Implementation quantities Because computers are finite, C + +

Why does an empty declaration work for definitions with int arguments but not for float arguments?

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问题 I thought the difference is that declaration doesn't have parameter types... Why does this work: int fuc(); int fuc(int i) { printf("%d", i); return 0; } but this fails compiling: int fuc(); int fuc(float f) { printf("%f", f); return 0; } with the message: error: conflicting types for ‘fuc’. note: an argument type that has a default promotion can’t match an empty parameter name list declaration 回答1: A declaration: int f(); ...tells the compiler that some identifier ( f , in this case) names a

Why do functions need to be declared before they are used?

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问题 When reading through some answers to this question, I started wondering why the compiler actually does need to know about a function when it first encounters it. Wouldn\'t it be simple to just add an extra pass when parsing a compilation unit that collects all symbols declared within, so that the order in which they are declared and used does not matter anymore? One could argue, that declaring functions before they are used certainly is good style, but I am wondering, is there are any other

Finding out which functions are called within a given function [duplicate]

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问题 Possible Duplicate: Generating a Call Graph in R I\'d like to systematically analyze a given function to find out which other functions are called within that very function. If possible, recursively. I came across this function in a blog post by milktrader with which I can do something similar for packages (or namespaces) listFunctions <- function( name, ... ){ name.0 <- name name <- paste(\"package\", \":\", name, sep=\"\") if (!name %in% search()) { stop(paste(\"Invalid namespace: \'\",

Why can't I define a function inside another function?

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问题 This is not a lambda function question, I know that I can assign a lambda to a variable. What\'s the point of allowing us to declare, but not define a function inside code? For example: #include <iostream> int main() { // This is illegal // int one(int bar) { return 13 + bar; } // This is legal, but why would I want this? int two(int bar); // This gets the job done but man it\'s complicated class three{ int m_iBar; public: three(int bar):m_iBar(13 + bar){} operator int(){return m_iBar;} };