无法让setter工作

Question

代码:

HEADER

class Parser{

private:
    unsigned int cant_documentos;
    unsigned int cant_terminos;
    std::map<std::string,short> dicc_stopwords;
    std::map<std::string,unsigned int> hash_frecuencias_globales;
    std::map<std::string,std::map<std::string,unsigned int> > hash_frecuencias_locales;
    std::map<std::string,std::string> hash_apariciones_unicas;
public:
    Parser();
    ~Parser();


public:
    void setFrecuenciasGlobales(std::map<std::string,std::map<std::string,unsigned int> > frecuencias);
};

头顶

.CPP

void Parser::setFrecuenciasGlobales(map<string,map<string,unsigned int> > frecuencias){
hash_frecuencias_globales = frecuencias;
cant_terminos = frecuencias.size();
}

CPP结束

编译器输出:

parser/parser.cpp:102:30: error: no match for ‘operator=’ in ‘((Parser*)this)->Parser::hash_frecuencias_globales = frecuencias’
parser/parser.cpp:102:30: note: candidate is:
/usr/include/c++/4.6/bits/stl_map.h:253:7: note: std::map<_Key, _Tp, _Compare, _Alloc>& std::map<_Key, _Tp, _Compare, _Alloc>::operator=(const std::map<_Key, _Tp, _Compare, _Alloc>&) [with _Key = std::basic_string<char>, _Tp = unsigned int, _Compare = std::less<std::basic_string<char> >, _Alloc = std::allocator<std::pair<const std::basic_string<char>, unsigned int> >, std::map<_Key, _Tp, _Compare, _Alloc> = std::map<std::basic_string<char>, unsigned int>]
/usr/include/c++/4.6/bits/stl_map.h:253:7: note:   no known conversion for argument 1 from ‘std::map<std::basic_string<char>, std::map<std::basic_string<char>, unsigned int> >’ to ‘const std::map<std::basic_string<char>, unsigned int>&’

问题出在哪儿？

Answer 1

hash_frecuencias_globales是一个std::map<std::string,unsigned int>,你试图给std::map<std::string,std::map<std::string,unsigned int> >它分配一个:

void Parser::setFrecuenciasGlobales(map<string,map<string,unsigned int> > frecuencias){
  hash_frecuencias_globales = frecuencias; // oops!

至于frequencias通过价值传递,这只有在你离开它或打电话时才有意义std::map::swap.对于简单的赋值,最好通过const引用传递并避免不必要的副本.