C - Committee Draft of ISO9899:TC2

Peter Kitson

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Sample Chapter From C - Committee Draft of ISO9899:TC2
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5.1.1.1 Program structure


A C program need not all be translated at the same time. The text of the program is kept
in units called source files, (or preprocessing files) in this International Standard. A
source file together with all the headers and source files included via the preprocessing
directive #include is known as a preprocessing translation unit. After preprocessing, a
preprocessing translation unit is called a translation unit. Previously translated translation
units may be preserved individually or in libraries. The separate translation units of a
program communicate by (for example) calls to functions whose identifiers have external
linkage, manipulation of objects whose identifiers have external linkage, or manipulation
of data files. Translation units may be separately translated and then later linked to
produce an executable program.

5.1.1.2 Translation phases


The precedence among the syntax rules of translation is specified by the following
phases.)
1. Physical source file multibyte characters are mapped, in an implementationdefined
manner, to the source character set (introducing new-line characters for
end-of-line indicators) if necessary. Trigraph sequences are replaced by
corresponding single-character internal representations.

2. Each instance of a backslash character (\) immediately followed by a new-line
character is deleted, splicing physical source lines to form logical source lines.
Only the last backslash on any physical source line shall be eligible for being part
of such a splice. A source file that is not empty shall end in a new-line character,
which shall not be immediately preceded by a backslash character before any such
splicing takes place.

3. The source file is decomposed into preprocessing tokens) and sequences of
white-space characters (including comments). A source file shall not end in a
partial preprocessing token or in a partial comment. Each comment is replaced by
one space character. New-line characters are retained. Whether each nonempty
sequence of white-space characters other than new-line is retained or replaced by
one space character is implementation-defined.

4. Preprocessing directives are executed, macro invocations are expanded, and
_Pragma unary operator expressions are executed. If a character sequence that
matches the syntax of a universal character name is produced by token
concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing
directive causes the named header or source file to be processed from phase 1
through phase 4, recursively. All preprocessing directives are then deleted.

5. Each source character set member and escape sequence in character constants and
string literals is converted to the corresponding member of the execution character
set; if there is no corresponding member, it is converted to an implementationdefined
member other than the null (wide) character.)

6. Adjacent string literal tokens are concatenated.

7. White-space characters separating tokens are no longer significant. Each
preprocessing token is converted into a token. The resulting tokens are
syntactically and semantically analyzed and translated as a translation unit.

8. All external object and function references are resolved. Library components are
linked to satisfy external references to functions and objects not defined in the
current translation. All such translator output is collected into a program image
which contains information needed for execution in its execution environment.