If the function has been declared and defined, then the only remaining issue is scope, i.e. visibility.
Ideally, functions should only be declared in a header and defined in a translation unit (source file) that includes the header. However, trivial functions are often defined in a header as they are usually good candidates for inline expansion, but you must remember to declare the function inline. Often it is better to forward declare inline functions so that maintainers are not distracted by the implementation details which can be placed towards the end of the header, out of the way. However, a definition is also a declaration, so forward declaring an inline function is not a requirement unless there is a cyclic dependency issue where a forward declaration is necessary to break the cycle.
A variable declared static outside of a function has a scope the of the source file only. It is not a global variable. A variable declared outside of a function and without the static qualifier would be a global variable.
All function interfaces must be declared before they can be used. This is known as a forward declaration and is strictly enforced in C++ (but not in C). To facilitate this, interfaces are typically placed in a header file which can then be included in every source file that requires access to that function. The interface need not be defined (implemented) in the header unless the function is a template function. Typically, implementations are kept separate from interfaces (template function implementations are kept in the header but typically separated from the interface) since the interface contains everything the user needs to know in order to make use of the function.
If you want to use prototype it has to be declared before main(). If you have a function of type double with one argument of type int (with name arg), and the function name is func, then we have:#include ...double func(int arg);...int main(...){...return 0;}...double func(int arg){...}
The execution of the program starts with function main, wherever it is in the source.
What function do you mean? Any function defined in a source file? Or any function used in a source file? Be more specific.
Ideally, functions should only be declared in a header and defined in a translation unit (source file) that includes the header. However, trivial functions are often defined in a header as they are usually good candidates for inline expansion, but you must remember to declare the function inline. Often it is better to forward declare inline functions so that maintainers are not distracted by the implementation details which can be placed towards the end of the header, out of the way. However, a definition is also a declaration, so forward declaring an inline function is not a requirement unless there is a cyclic dependency issue where a forward declaration is necessary to break the cycle.
A variable declared static outside of a function has a scope the of the source file only. It is not a global variable. A variable declared outside of a function and without the static qualifier would be a global variable.
There are no 'sections' in C source, you can define functions anywhere, except inside another function or variable/type definition.
All function interfaces must be declared before they can be used. This is known as a forward declaration and is strictly enforced in C++ (but not in C). To facilitate this, interfaces are typically placed in a header file which can then be included in every source file that requires access to that function. The interface need not be defined (implemented) in the header unless the function is a template function. Typically, implementations are kept separate from interfaces (template function implementations are kept in the header but typically separated from the interface) since the interface contains everything the user needs to know in order to make use of the function.
the function of a power source in a circuit is that it provides a steady source of static electricity
the function of a power source in a circuit is that it provides a steady source of static electricity
If you want to use prototype it has to be declared before main(). If you have a function of type double with one argument of type int (with name arg), and the function name is func, then we have:#include ...double func(int arg);...int main(...){...return 0;}...double func(int arg){...}
A lamp is a light source that enables you to see where you are going in darkness.
The execution of the program starts with function main, wherever it is in the source.
The banana peel can be an alternative source of biodiesel. It has the properties which enables it to compensate with the standard we use.
A function prototype is just another name for a function declaration which essentially describes the function's interface (as opposed to its implementation). The declaration must include the name of the function, the number and type of its arguments (if any) and the return type. Formal argument names are not required in a prototype, nor is the implementation, but the implementation must be defined somewhere, whether it is in an external library which links to your program, a separate source file within your program, or implicitly inline expanded within the prototype itself. Prototypes are typically placed in a header file while the implementation is placed in a corresponding source file. Separating interfaces from implementations in this manner modularises your code. When you need to make use of a function, you simply include the header that contains the prototype. The prototype provides all the information required in order to use the function, and tells the compiler all it needs to know in order to match the interface with its definition. Prototypes are also used to forward declare functions. In C++, a function must be declared before it can be used, even if the function is not fully defined at the point it is first used. By placing prototypes in a header, the programmer does not have to look up the prototype in order to write a forward declaration, he simply includes the header that contains the prototype itself. When you include a header it's just as if you'd copy/pasted the entire contents of that header into your source code at the point of inclusion. Note that templates must be fully-defined before they can be used. Typically the definition is placed in the same file as the prototype (in some cases inline expanded), but you can also include the definition file in the prototype header in order to modularise interfaces and implementations. Note also that the definition of a function is also a declaration of that same function, even if it was forward declared. However, there can only ever be one forward declaration and one definition at most of any one function (the "one definition rule", or ODR). This presents a problem when you have several source files that all require access to the same function prototype, since you'd effectively be declaring the function once for each inclusion. This problem is resolved by using inclusion guards in the header. An inclusion guard is a compiler directive that ensures a file is only ever included once in any compilation. A typical inclusion guard for a file named MyHeader.h is as follows: #ifndef _MY_HEADER_H_ #define _MY_HEADER_H_ // actual content of header goes here #endif _MY_HEADER_H_ The first time this file is included, the _MY_HEADER_H_ symbol will not be defined, so the compiler defines it and then includes the content in your source file. The next time the file is included, the compiler will see that it has already defined _MY_HEADER_H_, thus everything up to the corresponding #endif _MY_HEADER_H_ at the end of the file is completely ignored. The definition must also appear just once in your source. Although the definition is itself a declaration, the compiler knows that if a function declaration has not been defined then it must be a prototype or forward declaration, and will use the prototype to match the declaration with its definition. But once defined, it cannot subsequently be redefined.