Keywords are words that have special meaning to the compiler and may not be used as identifiers.

While we have extensive leeway with respect to the names we can use for identifiers, there are some words that cannot under any circumstances be used as identifiers. These are known as keywords.

ANSI C Keywords

auto break case char
const continue default do
double else enum extern
float for goto if
int long register return
short signed sizeof static
struct switch typedef union
unsigned void volatile while

These 32 keywords have specific meanings in ANSI C and as such, may not be used for anything other than their intended purpose. In any ANSI C implementation, these keywords will have the exact same meanings which we will explore throughout the rest of this class. However, some compilers deviate from the standard ANSI implementation resulting in potential differences in the behavior of some keywords.

Some compiler implementations may define additional keywords. While these extra keywords are not part of the ANSI C standard, they will have the same restrictions as the ANSI keywords in their compiler tool chain. The Microchip MPLAB® XC16 compiler, for example, defines 12 additional keywords. These and any other compiler specific keywords will be covered in the compiler classes.

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