编译错误：调用基类型构造函数时无效转换

Question

我想在MinGW-64 lljvm下编译一个不太大的程序。但是我陷入了一个让我疯狂的错误。

的代码如下：

backend.h

class JVMWritter { 
... 
static char id; 
... 
}; 

backend.cpp

char JVMWriter::id = 0; 

JVMWriter::JVMWriter(): FunctionPass(&id) {} 

现在，FunctionPass声明中Pass.h这样的：

Pass.h

class FunctionPass { 
... 
explicit FunctionPass (char &pid) : <initialization here> {} 
... 
}; 

当我尝试编译，我不断收到以下错误：

backend.cpp:39:16: error: invalid conversion from 'char*' to 'char' [-fpermissive] 
    FunctionPass(&JVMWriter::id), targetData(td), out(o), classname(cls), debug(dbg) { 
       ^~~~~~~~~~ 

In file included from D:/dev/msys64/mingw64/include/llvm/IR/DataLayout.h:27:0, 
       from D:/dev/msys64/mingw64/include/llvm/IR/Module.h:20, 
       from D:/dev/msys64/mingw64/include/llvm/IR/PassManager.h:46, 
       from D:/dev/msys64/mingw64/include/llvm/Analysis/LoopInfo.h:47, 
       from backend.h:29, 
       from backend.cpp:23: 
D:/dev/msys64/mingw64/include/llvm/Pass.h:300:12: note: initializing argument 1 of 'llvm::FunctionPass::FunctionPass(char&)' 
    explicit FunctionPass(char &pid) : Pass(PT_Function, pid) {} 
      ^~~~~~~~~~~~ 

backend.cpp:39:16: error: cannot bind rvalue '(char)(& JVMWriter::id)' to 'char&' 
    FunctionPass(&JVMWriter::id), targetData(td), out(o), classname(cls), debug(dbg) { 
       ^~~~~~~~~~ 

In file included from D:/dev/msys64/mingw64/include/llvm/Pass.h:388:0, 
       from D:/dev/msys64/mingw64/include/llvm/IR/DataLayout.h:27, 
       from D:/dev/msys64/mingw64/include/llvm/IR/Module.h:20, 
       from D:/dev/msys64/mingw64/include/llvm/IR/PassManager.h:46, 
       from D:/dev/msys64/mingw64/include/llvm/Analysis/LoopInfo.h:47, 
       from backend.h:29, 
       from backend.cpp:23: 
D:/dev/msys64/mingw64/include/llvm/PassAnalysisSupport.h: In instantiation of 'llvm::AnalysisUsage& llvm::AnalysisUsage::addRequired() [with PassClass = llvm::LoopInfo]': 

backend.cpp:52:27: required from here 
D:/dev/msys64/mingw64/include/llvm/PassAnalysisSupport.h:61:39: error: 'ID' is not a member of 'llvm::LoopInfo' 
    return addRequiredID(PassClass::ID); 

我明显的问题：为什么是抱怨我在尝试一个非有效转换？我在这些片断中看不到这样的企图。

Answer 1

char & pid声明pid以char的引用，而传递&id这是一个指向char。

Answer 2

将FunctionPass(&id)替换为FunctionPass(id)。