修复一个由宏引起的rapidjson编译失败问题

问题描述

项目本身可以编译成功，由于使用了rapidjson而引入了如下三个头文件

#include "rapidjson/document.h"
#include "rapidjson/stringbuffer.h"
#include "rapidjson/prettywriter.h"

此时编译后出现以下错误（只挑选了关键的）

bc_out/public/protobuf-json/output/include/rapidjson/reader.h: At global scope:
bc_out/public/protobuf-json/output/include/rapidjson/reader.h:84: error: expected unqualified-id before "unsigned"
bc_out/public/protobuf-json/output/include/rapidjson/reader.h:84: error: expected `)' before "unsigned"
bc_out/public/protobuf-json/output/include/rapidjson/reader.h: In member function `void rapidjson::GenericReader<SourceEncoding,TargetEncoding,Allocator>::ParseNumber(InputStream&,Handler&)':
bc_out/public/protobuf-json/output/include/rapidjson/reader.h:632: error: expected unqualified-id before '(' token
bc_out/public/protobuf-json/output/include/rapidjson/reader.h:632: error: expected primary-expression before "unsigned"
In file included from baidu/xfire/xcore2/plugins/material_search/src/material_search_proc_query_db.cpp:15:
bc_out/public/protobuf-json/output/include/rapidjson/document.h: In member function `const rapidjson::GenericValue<Encoding,Allocator>& rapidjson::GenericValue<Encoding,Allocator>::Accept(Handler&) const':
bc_out/public/protobuf-json/output/include/rapidjson/document.h:549: error: expected unqualified-id before '(' token
bc_out/public/protobuf-json/output/include/rapidjson/document.h:549: error: expected primary-expression before "unsigned"
bc_out/public/protobuf-json/output/include/rapidjson/document.h: At global scope:
bc_out/public/protobuf-json/output/include/rapidjson/document.h:791: error: expected unqualified-id before "unsigned"
bc_out/public/protobuf-json/output/include/rapidjson/document.h:791: error: expected `)' before "unsigned"
In file included from bc_out/public/protobuf-json/output/include/rapidjson/prettywriter.h:4,from baidu/xfire/xcore2/plugins/material_search/src/material_search_proc_query_db.cpp:17:
bc_out/public/protobuf-json/output/include/rapidjson/writer.h:45: error: expected unqualified-id before "unsigned"
bc_out/public/protobuf-json/output/include/rapidjson/writer.h:45: error: expected `)' before "unsigned"
bc_out/public/protobuf-json/output/include/rapidjson/writer.h:45: error: abstract declarator `rapidjson::Writer<OutputStream,SourceEncoding,Allocator>&' used as declaration
bc_out/public/protobuf-json/output/include/rapidjson/writer.h:45: error: expected `;' before "unsigned"
bc_out/public/protobuf-json/output/include/rapidjson/writer.h:46: error: expected `;' before "Writer"
In file included from baidu/xfire/xcore2/plugins/material_search/src/material_search_proc_query_db.cpp:17:
bc_out/public/protobuf-json/output/include/rapidjson/prettywriter.h:46: error: expected unqualified-id before "unsigned"
bc_out/public/protobuf-json/output/include/rapidjson/prettywriter.h:46: error: expected `)' before "unsigned"
bc_out/public/protobuf-json/output/include/rapidjson/prettywriter.h:46: error: abstract declarator `rapidjson::PrettyWriter<OutputStream,Allocator>&' used as declaration
bc_out/public/protobuf-json/output/include/rapidjson/prettywriter.h:46: error: expected `;' before "unsigned"
bc_out/public/protobuf-json/output/include/rapidjson/prettywriter.h:47: error: expected `;' before "PrettyWriter"

直接的意思是说reader.h头文件出错了，但显然rapid库本身没有错。

分析解决

reader.h出问题的代码84行如下：

void Uint(unsigned i);

定义了一个Uint的函数，根据经验有可能是某个地方也定义了相同的函数，且命名空间相同导致冲突，经过查找并没有，这时google到github上有人提出类似问题。可能是宏和Uint冲突了，于是做如下修改

#ifdef Uint
#undef Uint
#include "rapidjson/document.h"
#include "rapidjson/stringbuffer.h"
#include "rapidjson/prettywriter.h"
#endif

此时编译可以通过，但是毕竟我们强行undef了一个宏的定义，于是在依赖的文件中搜索Uint宏的定义

find . -name "*.h" | xargs grep "#define Uint"

./bc_out/lib2-64/ullib/output/include/ul_def.h:#define Uint(inp) (unsigned int)(inp)
./lib2-64/ullib/include/ul_def.h:#define Uint(inp) (unsigned int)(inp)

找到了该宏的定义，最后把其补充上，防止某些地方出现问题，最终解决后引用修改如下

#ifdef Uint
#undef Uint
#include "rapidjson/document.h"
#include "rapidjson/stringbuffer.h"
#include "rapidjson/prettywriter.h"
#define Uint(inp) (unsigned int)(inp)
#endif

此时编译通过，并且可以顺利执行。

BTW rapid json的确比Boost快，8w行的数据，boost用了近30s，rapid只用了不到2s。

补充

了解到了宏是全局作用的，所以就会和其他函数、变量冲突，对于函数，还有个解决方案是，把函数名用括号括起来，比如

(std::min)(x,y); 

此时min就不会被其他的定义为min的宏覆盖。 当然，这只对自己的代码有用，对于第三方库就不能这个改了。