标准迭代器分配错误

Question

Please bear with me if the question is silly.

The following are defined in a header file :

typedef char NAME_T[40];

struct NAME_MAPPING_T
{
    NAME_T englishName;
    NAME_T frenchName;
};

typedef std::vector<NAME_MAPPING_T> NAMES_DATABASE_T;

Later the need comes that a particular english name be found :

const NAMES_DATABASE_T *wordsDb;

string str;

std::find_if(   wordsDb->begin(), 
                wordsDb->end(), 
                [str](const NAME_MAPPING_T &m) -> bool { return strncmp(m.englishName, str.c_str(), sizeof(m.englishName)) == 0; } );

This code (which I copy-pasted to be honest) compiles, but if I want to check the value returned by find_if(), like this :

NAMES_DATABASE_T::iterator it;
it = std::find_if(blah ..)

the code will NOT compile !

In effect the line it = std::find_if(...) will return the error :

error C2679: binary '=' : no operator found which takes a right-hand operand of type 'std::_Vector_const_iterator<_Myvec>' (or there is no acceptable conversion)

What is wrong ?

Thanks for your time.

Answer 1

const NAMES_DATABASE_T *wordsDb;

Your wordsDb is const, therefore wordsDb->begin() returns a const iterator, therefore find_if returns a const iterator as well. You're trying to assign that const iterator to the non-const NAMES_DATABASE_T::iterator it , hence the error.

You can use NAMES_DATABASE_T::const_iterator to get a const iterator. And you should use std::string instead of those char buffers, unless there are some rare circumstances that require otherwise.