View source for Chapter 0: C Language Features ← Chapter 0: C Language Features

Keywords in C[edit]

Keywords are reserved words in C, which a programmer must not use for other purposes. In C11 standard there are totally 44 keywords which are as follows:

Language limits[edit]

Any C compiler (conforming to C11 standard) should be able to handle the following cases:

• 127 nesting levels of blocks
• 63 nesting levels of conditional inclusion
• 63 nesting levels of parenthesized declarators within a full declarator
• 63 nesting levels of parenthesized expressions within a full expression
• 63 significant initial characters in an internal identifier or a macro name
• 31 significant initial characters in an external identifier
• 4095 external identifiers in one translation unit
• 511 identifiers with block scope declared in one block
• 4095 macro identifiers simultaneously defined in one preprocessing translation unit
• 127 parameters in one function definition
• 127 arguments in one function call
• 127 parameters in one macro definition
• 127 arguments in one macro invocation
• 4095 characters in a logical source line
• 4095 characters in a string literal (after concatenation)
• 65535 bytes in an object (in a hosted environment only)
• 15 nesting levels for #included files
• 1023 case labels for a switch statement (excluding those for any nested switch

statements)

• 1023 members in a single structure or union
• 1023 enumeration constants in a single enumeration
• 63 levels of nested structure or union definitions in a single struct-declaration-list