| title | description | ms.date | helpviewer_keywords | ms.assetid | ||
|---|---|---|---|---|---|---|
Preprocessor grammar summary (C/C++) |
Defines and describes the Microsoft C/C++ compiler (MSVC) preprocessor grammar syntax. |
08/29/2019 |
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0acb6e9b-364c-4ef8-ace4-7be980521121 |
This article describes the formal grammar of the C and C++ preprocessor. It covers the syntax of preprocessing directives and operators. For more information, see Preprocessor and Pragma directives and the __pragma keyword.
Terminals are endpoints in a syntax definition. No other resolution is possible. Terminals include the set of reserved words and user-defined identifiers.
Nonterminals are placeholders in the syntax. Most are defined elsewhere in this syntax summary. Definitions can be recursive. The following nonterminals are defined in the Lexical Conventions section of the C++ Language Reference:
constant, constant-expression, identifier, keyword, operator, punctuator
An optional component is indicated by the subscripted opt. For example, the following syntax indicates an optional expression enclosed in curly braces:
{ expressionopt }
The conventions use different font attributes for different components of the syntax. The symbols and fonts are as follows:
| Attribute | Description |
|---|---|
| nonterminal | Italic type indicates nonterminals. |
| #include | Terminals in bold type are literal reserved words and symbols that must be entered as shown. Characters in this context are always case sensitive. |
| opt | Nonterminals followed by opt are always optional. |
| default typeface | Characters in the set described or listed in this typeface can be used as terminals in statements. |
A colon (:) following a nonterminal introduces its definition. Alternative definitions are listed on separate lines.
In code syntax blocks, these symbols in the default typeface have a special meaning:
| Symbol | Description |
|---|---|
| [ ] | Square brackets surround an optional element. |
| { | } | Curly braces surround alternative elements, separated by vertical bars. |
| ... | Indicates the previous element pattern can be repeated. |
In code syntax blocks, commas (,), periods (.), semi-colons (;), colons (:), parentheses (( )), double-quotes ("), and single-quotes (') are literals.
control-line:
#define identifier token-stringopt
#define identifier ( identifieropt , ... , identifieropt ) token-stringopt
#include "path-spec"
#include <path-spec>
#line digit-sequence "filename"opt
#undef identifier
#error token-string
#pragma token-string
constant-expression:
defined( identifier )
defined identifier
any other constant expression
conditional:
if-part elif-partsopt else-partopt endif-line
if-part:
if-line text
if-line:
#if constant-expression
#ifdef identifier
#ifndef identifier
elif-parts:
elif-line text
elif-parts elif-line text
elif-line:
#elif constant-expression
else-part:
else-line text
else-line:
#else
endif-line:
#endif
digit-sequence:
digit
digit-sequence digit
digit: one of
0 1 2 3 4 5 6 7 8 9
token-string:
String of tokens
token:
keyword
identifier
constant
operator
punctuator
filename:
Legal operating system filename
path-spec:
Legal file path
text:
Any sequence of text
Note
The following nonterminals are expanded in the Lexical conventions section of the C++ Language Reference: constant, constant-expression, identifier, keyword, operator, and punctuator.