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cpp.texi: Clarify documentation of relationship between #line and #include. 

* doc/cpp.texi: Clarify documentation of relationship between
	#line and #include.

From-SVN: r50209
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Zack Weinberg 2002-03-01 22:20:31 +00:00 committed by Zack Weinberg
parent b057b2130d
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2 changed files with 42 additions and 1 deletions
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@ -1,3 +1,8 @@
2002-03-01 Zack Weinberg <zack@codesourcery.com>
* doc/cpp.texi: Clarify documentation of relationship between
#line and #include.
2002-02-28 Richard Henderson <rth@redhat.com>
* expmed.c (store_bit_field): Prevent generation of CONCATs;

38
gcc/doc/cpp.texi
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@ -3044,7 +3044,35 @@ The result should match one of the above two forms.
@samp{#line} directives alter the results of the @code{__FILE__} and
@code{__LINE__} predefined macros from that point on. @xref{Standard
Predefined Macros}. They do not have any effect on @samp{#include}'s
idea of the directory containing the current file.
idea of the directory containing the current file. This is a change
from GCC 2.95. Previously, a file reading
@smallexample
#line 1 "../src/gram.y"
#include "gram.h"
@end smallexample
would search for @file{gram.h} in @file{../src}, then the @option{-I}
chain; the directory containing the physical source file would not be
searched. In GCC 3.0 and later, the @samp{#include} is not affected by
the presence of a @samp{#line} referring to a different directory.
We made this change because the old behavior caused problems when
generated source files were transported between machines. For instance,
it is common practice to ship generated parsers with a source release,
so that people building the distribution do not need to have yacc or
Bison installed. These files frequently have @samp{#line} directives
referring to the directory tree of the system where the distribution was
created. If GCC tries to search for headers in those directories, the
build is likely to fail.
The new behavior can cause failures too, if the generated file is not
in the same directory as its source and it attempts to include a header
which would be visible searching from the directory containing the
source file. However, this problem is easily solved with an additional
@option{-I} switch on the command line. The failures caused by the old
semantics could sometimes be corrected only by editing the generated
files, which is difficult and error-prone.
@node Pragmas
@chapter Pragmas
@ -3780,6 +3808,14 @@ were still available in traditional mode. It is now a separate program
and does not implement any of the GNU extensions, except for a partial
implementation of assertions. Even those may be removed in a future
release.
@item @samp{#line} and @samp{#include}
The @samp{#line} directive used to change GCC's notion of the
``directory containing the current file,'' used by @samp{#include} with
a double-quoted header file name. In 3.0 and later, it does not.
@xref{Line Control}, for further explanation.
@end itemize
@node Invocation