Compound Statement (C)

A compound statement (also called a "block") typically appears as the body of another statement, such as the if statement. Declarations and Types describes the form and meaning of the declarations that can appear at the head of a compound statement.

Syntax

compound-statement:
 { declaration-list_opt statement-list_opt }

declaration-list:
 declaration
 declaration-list declaration

statement-list:
 statement
 statement-list statement

If there are declarations, they must come before any statements. The scope of each identifier declared at the beginning of a compound statement extends from its declaration point to the end of the block. It's visible throughout the block unless a declaration of the same identifier exists in an inner block.

Identifiers in a compound statement are presumed auto unless explicitly declared otherwise with register, static, or extern, except functions, which can only be extern. You can leave off the extern specifier in function declarations and the function will still be extern.

Storage isn't allocated and initialization isn't permitted if a variable or function is declared in a compound statement with storage class extern. The declaration refers to an external variable or function defined elsewhere.

Variables declared in a block with the auto or register keyword are reallocated and, if necessary, initialized each time the compound statement is entered. These variables are no longer defined after the compound statement is exited. If a variable declared inside a block has the static attribute, the variable is initialized when program execution begins and keeps its value throughout the program. See Storage Classes for information about static.

This example illustrates a compound statement:

if ( i > 0 )
{
    line[i] = x;
    x++;
    i--;
}

In this example, if i is greater than 0, all statements inside the compound statement are executed in order.

See also

Statements