Summary: Qualifiers

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Keywords

Use the following keywords to qualify variables :

 const, volatile

General Comments

A qualifier constrains a variable's ability to be modified. A const variable, after it's initialized , can't be altered . The compiler can't assume that a volatile variable hasn't been changed by some outside agency, such as a hardware update.

Properties

Note

The declaration

 const int joy = 101;

establishes that the value of joy is fixed at 101 .

The declaration

 volatile unsigned int incoming;

establishes that the value of incoming might change between one occurrence of incoming in a program and its next occurrence.

The declaration

 const int * ptr = &joy;

establishes that the pointer ptr can't be used to alter the value of the variable joy . The pointer can, however, be made to point to another location. The declaration

 int * const ptr = &joy;

establishes that the pointer ptr can't have its value changed; that is, it can point only to joy . However, it can be used to alter joy .

The prototype

 void simple (const char * s);

establishes that after the formal argument s is initialized to whatever value is passed to simple() in a function call, sample() may not alter the value to which s points.

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