Summary of Lifetime and Visibility
The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.
The latest version of this topic can be found at Summary of Lifetime and Visibility.
The following table is a summary of lifetime and visibility characteristics for most identifiers. The first three columns give the attributes that define lifetime and visibility. An identifier with the attributes given by the first three columns has the lifetime and visibility shown in the fourth and fifth columns. However, the table does not cover all possible cases. Refer to Storage Classes for more information.
Summary of Lifetime and Visibility
| Attributes: Level | Item | Storage-Class Specifier | Result: Lifetime | Visibility |
|---|---|---|---|---|
| File scope | Variable definition | static | Global | Remainder of source file in which it occurs |
| Variable declaration | extern | Global | Remainder of source file in which it occurs | |
| Function prototype or definition | static | Global | Single source file | |
| Function prototype | extern | Global | Remainder of source file | |
| Block scope | Variable declaration | extern | Global | Block |
| Variable definition | static | Global | Block | |
| Variable definition | auto or register | Local | Block |
Description
The following example illustrates blocks, nesting, and visibility of variables:
Code
// Lifetime_and_Visibility.c
#include <stdio.h>
int i = 1; // i defined at external level
int main() // main function defined at external level
{
printf_s( "%d\n", i ); // Prints 1 (value of external level i)
{ // Begin first nested block
int i = 2, j = 3; // i and j defined at internal level
printf_s( "%d %d\n", i, j ); // Prints 2, 3
{ // Begin second nested block
int i = 0; // i is redefined
printf_s( "%d %d\n", i, j ); // Prints 0, 3
} // End of second nested block
printf_s( "%d\n", i ); // Prints 2 (outer definition
// restored)
} // End of first nested block
printf_s( "%d\n", i ); // Prints 1 (external level
// definition restored)
return 0;
}
Comments
In this example, there are four levels of visibility: the external level and three block levels. The values are printed to the screen as noted in the comments following each statement.