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

Example

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.

See Also

Concepts

Lifetime, Scope, Visibility, and Linkage