您好，我正在尝试将 Flex 与 C++ 结合使用。阅读 Flex 手册后，我开始编写一个小示例来构建我的项目。
我最初想出了这个小例子。
#include <string.h>
#include <iostream>
#include <sstream>
#include <string>
#include <streambuf>
#include <fstream>
int main() {
std::string stringvalues = "TOKEN TEST 123";
std::istringstream inputStringStream(stringvalues);
std::istream& inputStream = inputStringStream;
std::ofstream outputStream("test.txt");
yyFlexLexer myTest(inputStream, outputStream);
}
在构建文件夹内，当我执行
cmake ..makealfredo@alfredo-ThinkPad-T440p:~/repos/FlexCpp/build$ make
[ 20%] Linking CXX static library libkeywords.a
[ 20%] Built target keywords
[ 40%] Building CXX object src/back-end/CMakeFiles/Foo.dir/main.cpp.o
/home/alfredo/repos/FlexCpp/src/back-end/main.cpp: In function ‘int main()’:
/home/alfredo/repos/FlexCpp/src/back-end/main.cpp:17:5: error: ‘yyFlexLexer’ was not declared in this scope
17 | yyFlexLexer myTest(inputStream, outputStream);
| ^~~~~~~~~~~
make[2]: *** [src/back-end/CMakeFiles/Foo.dir/build.make:80: src/back-end/CMakeFiles/Foo.dir/main.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:126: src/back-end/CMakeFiles/Foo.dir/all] Error 2
make: *** [Makefile:91: all] Error 2
奇怪的是，如果我注释掉main.cpp中的最后一行
//yyFlexLexer myTest(inputStream, outputStream);
我收到以下错误：
lexer.l: In member function ‘virtual int yyFlexLexer::yylex()’:
lexer.l:172:1: error: ‘yypanic’ was not declared in this scope
/usr/local/flex/include/FlexLexer.h: At global scope:
/home/alfredo/repos/FlexCpp/src/back-end/lexer.yy.cc:49:25: error: redefinition of ‘class yyFlexLexer’
49 | #define yyFlexLexer yyFlexLexer
| ^~~~~~~~~~~
/home/alfredo/repos/FlexCpp/src/back-end/lexer.yy.cc:49:25: note: previous definition of ‘class yyFlexLexer’
49 | #define yyFlexLexer yyFlexLexer
| ^~~~~~~~~~~
make[2]: *** [src/back-end/CMakeFiles/Foo.dir/build.make:94: src/back-end/CMakeFiles/Foo.dir/lexer.yy.cc.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:126: src/back-end/CMakeFiles/Foo.dir/all] Error 2
make: *** [Makefile:91: all] Error 2
我的项目目录如下所示。
backend/
|- main.cpp (what you saw ealier)
|- CMakeLists.txt
|- keywords.hxx (contains enum tokens and struct)
|- lexer.l
|- lexer.yy.cc (this will be generated by lexer.l when we compile with c++
we set %option c++ in our lexer.l file )
这是我的 lexer.l 的样子
/* we dont have an interactive session. */
%option never-interactive
/* we will handle the nodefault rule. */
%option nodefault
/* we dont want yyinput() and yyunput(). */
%option noinput nounput
/* don't include <unistd.h> we dont need it. */
%option nounistd
/*
not needed for now, in the future when users can work
with multiple files we can start using it.
*/
%option noyywrap
/*
these two options are doubled to get more detailed reports.
write performance report to stderr.
*/
%option perf-report perf-report
/* write statistics summary to stderr. */
%option verbose verbose
/* generate warning messages for mistakes. */
%option warn
/* maintain current line number in yylineno. */
%option yylineno
%option c++
/* c items that can be used in the rules section */
%{
#include <stdio.h>
#include <keywords.hxx>
int iskeyword(char * keyword);
%}
digit [0-9]
exponent [ee][-+]?{digit}+
id_start [_a-za-z]
id_after {id_start}|{digit}
/*===================rules===================*/
%%
/* a bunch of rules */
%%
/*=================user-code=================*/
#include <keywords.hxx>
/*As mentioned by Flex manual we include this if our main() is not in this file */
#include <FlexLexer.h>
int iskeyword(char * keyword){
for(int index = 0; index < NUM_KEYWORDS; index++){
if(strcmp(keywords[index].keyWord, keyword)){
return keywords[index].token;
}
}
return 0;
}
CMakeLists.cmake
cmake_minimum_required(VERSION 3.5)
project(
TestingProj
)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -isystem /usr/local/flex/include")
find_package(FLEX REQUIRED)
add_library(keywords keywords.hxx)
set_target_properties(keywords PROPERTIES LINKER_LANGUAGE CXX)
target_include_directories(keywords PUBLIC ./)
FLEX_TARGET(
gen_lexer
lexer.l
lexer.yy.cc
)
add_executable(
Foo
main.cpp
${FLEX_gen_lexer_OUTPUTS}
)
target_link_libraries(Foo PUBLIC keywords)
target_link_libraries(Foo PUBLIC ${FLEX_LIBRARIES})
如果我记录以下内容
message("FLEX_FOUND ${FLEX_FOUND}")
message("FLEX_EXECUTABLE ${FLEX_EXECUTABLE}")
message("FLEX_VERSION ${FLEX_VERSION}")
message("FLEX_LIBRARIES ${FLEX_LIBRARIES}")
message("FLEX_INCLUDE_DIRS ${FLEX_INCLUDE_DIRS}")
我明白了
FLEX_FOUND TRUE
FLEX_EXECUTABLE /usr/local/flex/bin/flex
FLEX_VERSION 2.6.4
FLEX_LIBRARIES /usr/local/flex/lib/libfl.so
FLEX_INCLUDE_DIRS /usr/local/flex/include
我也厌倦了遵循 Flex 手册。没有帮助。
如果您想创建多个（不同的）词法分析器类，您可以使用“-P”标志（或 prefix= option) 将每个 yyFlexLexer 重命名为其他“xxFlexLexer”。然后是你 每个词法分析器类可以在其他源中包含
一次，首先重命名 yyFlexLexer如下： #undef yyFlexLexer #define yyFlexLexer xxFlexLexer #包括 #undef yyFlexLexer #define yyFlexLexer zzFlexLexer #包括
我不确定我做错了什么。我花了很多时间试图让 Flex 和 C++ 工作。我能够让 Flex 和纯 C 工作，但只是 C++ 我遇到了麻烦。截至发布时，我的最佳猜测是
FlexLexer.hFlexLexer.h/includeFlexLexer.h/usr/local/flex/include/FlexLexer.h:.cmake任何帮助将不胜感激。
我首先按照 Tysvarev 留下的评论解决了这个问题，我引用了他们。
“不需要显式包含 lexer.l 中的该文件。但是在 main.cpp 中，你需要包含 FlexLexer.h，否则编译器没有有关 yyFlexLexer 类的信息”
然后在
%{ ... %}void yypanic( char* errorMessage);
最后在我写的用户代码中
void yypanic(char * errorMessage) {
std::cout << errorMessage << std::endl;
}