declaration

Why does this code work in C but not in C++? int i = 5; int i; // but if I write int i = 5; again I get error in C also int main(){ // using i } Prasoon Saurav Tentative definition is allowed in C but not in C++. A tentative definition is any external data declaration that has no storage class specifier and no initializer. C99 6.9.2/2 A declaration of an identifier for an object that has file scope without an initializer , and without a storage-class specifier or with the storage-class specifier static , constitutes a tentative definition. If a translation unit contains one or more tentative

What’s the difference between “{}” and “[]” while declaring a JavaScript array? Normally I declare like var a=[]; What is the meaning of declaring the array as var a={} Nobody seems to be explaining the difference between an array and an object. [] is declaring an array. {} is declaring an object. An array has all the features of an object with additional features (you can think of an array like a sub-class of an object) where additional methods and capabilities are added in the Array sub-class. In fact, typeof [] === "object" to further show you that an array is an object. The additional

I keep seeing the "my" keyword in front of variable names in example Perl scripts online but I have no idea what it means. I tried reading the manual pages and other sites online but I'm having difficulty discerning what it is for given the difference between how I see it used and the manual. For example, its used to get the length of the array in this post: Find size of an array in Perl But the manual says: A my declares the listed variables to be local (lexically) to the enclosing block, file, or eval. If more than one value is listed, the list must be placed in parentheses. What does it do

When we design classes in Java, Vala, or C# we put the definition and declaration in the same source file. But in C++ it is traditionally preferred to separate the definition and declaration in two or more files. What happens if I just use a header file and put everything into it, like Java? Is there a performance penalty or something? The answer depends on what kind of class you're creating. C++'s compilation model dates back to the days of C, and so its method of importing data from one source file into another is comparatively primitive. The #include directive literally copies the contents

We can declare functions inside functions (I wanted a local variable, but it parses as a function declaration): struct bvalue; struct bdict { bdict(bvalue); } struct bvalue { explict operator bdict() const; } struct metainfo { metainfo(bdict); } void foo(bvalue v) { metainfo mi(bdict(v)); // parses as function declaration metainfo mi = bdict(v); // workaround // (this workaround doesn't work in the presence of explicit ctors) } Are the sole reasons "because it makes the parser simpler" and "because the standard says so", or is there an obscure use for this? This is really a C question, because

Possible Duplicate: Should C++ eliminate header files? In languages like C# and Java there is no need to declare (for example) a class before using it. If I understand it correctly this is because the compiler does two passes on the code. In the first it just "collects the information available" and in the second one it checks that the code is correct. In C and C++ the compiler does only one pass so everything needs to be available at that time. So my question basically is why isn't it done this way in C and C++. Wouldn't it eliminate the needs for header files? The short answer is that