std :: map具有结构错误值

Question

I use Visual Studio Express 2013 and I try to run this code:

struct opcode {
    int length; 
};

std::map<int, struct opcode> opcodes;

opcodes[0x20] = {
    3
};

I get this error: error C2040: 'opcodes' : 'int [32]' differs in levels of indirection from 'std::map<int,opcode,std::less<_Kty>,std::allocator<std::pair<const _Kty,_Ty>>>'

And when I hover over opcodes I get this this declaration has no storage class or type specifier .

SOLUTION

The problem of mine was that I have put the statement outside the function.

Answer 1

In C++ language statements - ie "the actual code" - have to reside inside functions. This

opcodes[0x20] = {
    3
};

is a statement. You cannot just throw it into a file without declaring a function. You cannot just write C++ code (ie statements) in the middle of the file.

All you can do in the "whitespace" between function is write declarations . So, you statement above was interpreted by the compiler as a declaration. Hence the strange error messages from the compiler.

If you intended this to be a statement, it should have looked as follows (for example)

int main()
{
  opcodes[0x20] = { 3 };    
}

However, you could achieve the same effect without a function by using an initializer , which is a part of declaration

std::map<int, struct opcode> opcodes = { { 0x20, { 3 } } };