diff options
Diffstat (limited to 'doc/autoconf.texi')
| -rw-r--r-- | doc/autoconf.texi | 68 |
1 files changed, 52 insertions, 16 deletions
diff --git a/doc/autoconf.texi b/doc/autoconf.texi index 2422bd67..3a026871 100644 --- a/doc/autoconf.texi +++ b/doc/autoconf.texi @@ -4195,37 +4195,73 @@ The result of the test can be overridden by setting the variable @end defmac @anchor{AC_PROG_LEX} -@defmac AC_PROG_LEX +@defmac AC_PROG_LEX (@var{options}) @acindex{PROG_LEX} @ovindex LEX @ovindex LEXLIB @cvindex YYTEXT_POINTER @ovindex LEX_OUTPUT_ROOT @caindex prog_LEX -If @code{flex} is found, set output variable @code{LEX} to @samp{flex}. -Otherwise set @code{LEX} to @samp{lex}, if found. -If neither variant is available, set @code{LEX} to @samp{:}; +Search for a lexical analyzer generator, preferring @code{flex} +to plain @code{lex}. Output variable @code{LEX} is set to whichever +program is available. If neither program is available, @code{LEX} +is set to @samp{:}; for packages that ship the generated @file{file.yy.c} alongside the source @file{file.l}, this default allows users without a lexer generator to still build the package even if the timestamp for @file{file.l} is inadvertently changed. -The result of this test can be influenced by setting the variable -@code{LEX} or the cache variable @code{ac_cv_prog_LEX}. +The name of the program to use can be overridden by setting the +output variable @code{LEX} or the cache variable @code{ac_cv_prog_LEX} +when running @command{configure}. + +If a lexical analyzer generator is found, this macro performs additional +checks for common portability pitfalls. If these additional checks +fail, @code{LEX} is reset to @samp{:}; otherwise the following +additional macros and variables are provided. -If either @code{flex} or @code{lex} is found, this macro performs -additional checks for common portability pitfalls. If these additional -checks fail, @code{LEX} is also set to @samp{:}. +Preprocessor macro @code{YYTEXT_POINTER} is defined if the lexer +skeleton, by default, declares @code{yytext} as a @samp{@w{char *}} +rather than a @samp{@w{char []}}. Output variable @code{LEX_OUTPUT_ROOT} is set to the base of the file name that the lexer generates; this is usually either @file{lex.yy} or -@file{lexyy}. Preprocessor macro @code{YYTEXT_POINTER} is defined if -the lexer skeleton, by default, declares @code{yytext} as a @samp{char -*} rather than a @samp{char []}. Finally, if generated lexers need a -library to work, set output variable @code{LEXLIB} to an option for that -library (e.g., @option{-ll}); otherwise define @code{LEXLIB} to empty. -A library that merely defines @code{main} and @code{yywrap} placeholder -functions is not considered to be needed. +@file{lexyy}. + +If generated lexers need a library to work, output variable +@code{LEXLIB} is set to a link option for that library (e.g., +@option{-ll}), otherwise it is set to empty. + +The @var{options} argument modifies the behavior of @code{AC_PROG_LEX}. +It should be a whitespace-separated list of options. Currently there +are only two options, and they are mutually exclusive: + +@table @code +@item yywrap +Indicate that the library in @code{LEXLIB} needs to define the function +@code{yywrap}. If a library that defines this function cannot be found, +@code{LEX} will be reset to @samp{:}. + +@item noyywrap +Indicate that the library in @code{LEXLIB} does not need to define the +function @code{yywrap}. @command{configure} will not search for it at +all. +@end table + +Prior to Autoconf 2.70, @code{AC_PROG_LEX} did not take any arguments, +and its behavior was different from either of the above possibilities: +it would search for a library that defines @code{yywrap}, and would set +@code{LEXLIB} to that library if it finds one. However, if a library +that defines this function could not be found, @code{LEXLIB} would be +left empty and @code{LEX} would @emph{not} be reset. This behavior was +due to a bug, but several packages came to depend on it, so +@code{AC_PROG_LEX} still does this if neither the @code{yywrap} nor the +@code{noyywrap} option is given. + +Usage of @code{AC_PROG_LEX} without choosing one of the @code{yywrap} +or @code{noyywrap} options is deprecated. It is usually better to +use @code{noyywrap} and define the @code{yywrap} function yourself, +as this almost always renders the @code{LEXLIB} unnecessary. @strong{Caution:} As a side-effect of the test, this macro may delete any file in the configure script's current working directory named |