Question

编辑：我在字符串声明中使用std::前缀减少了大部分错误。但是，一些函数似乎存在问题，特别是那些以字符串作为参数的函数的定义。

编辑＃2：更新了我的代码（我的DID在我的函数声明中有std::前缀，但在我的帖子中没有反映出来。在问题函数中为字符串参数添加std::前缀时，请查看底部显示的错误。

我有一个头文件movie.h，其中包含以下代码（相关代码）：

#include <string>

class Movie
{
    public:

        void addMovieName(std::string movie);
        void addLastName(std::string nameLast);
        void addFirstName(std::string nameFirst);

    private:

        string movieName,
               directorLastName,
               directorFirstName,
               directorFullName;
};

这样的实施文件movie.cpp（相关代码）：

#include "movie.h"

// addFirstName, addLastName, and addMovie name all do the same things
// so I'm only including one since they all generate the same error

void Movie::addFirstName(string nameFirst)
{
   directorFirstName = nameFirst.resize(10, ' ');
}

编译后，我收到以下错误：

g++ -c movie.cpp -o movie.o
movie.cpp:225: error: variable or field ‘addFirstName’ declared void
movie.cpp:225: error: ‘int Movie::addFirstName’ is not a static member of ‘class Movie’
movie.cpp:225: error: ‘string’ was not declared in this scope
movie.cpp:226: error: expected ‘,’ or ‘;’ before ‘{’ token
movie.cpp:240: error: variable or field ‘addLastName’ declared void
movie.cpp:240: error: ‘int Movie::addLastName’ is not a static member of ‘class Movie’
movie.cpp:240: error: ‘string’ was not declared in this scope
movie.cpp:241: error: expected ‘,’ or ‘;’ before ‘{’ token
movie.cpp:255: error: variable or field ‘addMovieName’ declared void
movie.cpp:255: error: ‘int Movie::addMovieName’ is not a static member of ‘class Movie’
movie.cpp:255: error: ‘string’ was not declared in this scope
movie.cpp:256: error: expected ‘,’ or ‘;’ before ‘{’ token
make: *** [movie.o] Error 1

有些人说我需要在函数定义中将std::添加到字符串参数中。

这样做：

// adding std:: prefix
void Movie::addFirstName(std::string nameFirst)
{
   directorFirstName = nameFirst.resize(10, ' ');
}

我收到以下错误。请注意，我只更改了一个功能。我不明白的第一个错误，而其余的仍然和以前一样。

g++ -c movie.cpp -o movie.o
movie.cpp: In member function ‘void Movie::addFirstName(std::string)’:
movie.cpp:227: error: no match for ‘operator=’ in ‘((Movie*)this)->Movie::directorFirstName = nameFirst.std::basic_string<_CharT, _Traits, _Alloc>::resize [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>](10u, 32)’
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/basic_string.h:485: note: candidates are: std::basic_string<_CharT, _Traits, _Alloc>& std::basic_string<_CharT, _Traits, _Alloc>::operator=(const std::basic_string<_CharT, _Traits, _Alloc>&) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/basic_string.h:493: note:                 std::basic_string<_CharT, _Traits, _Alloc>& std::basic_string<_CharT, _Traits, _Alloc>::operator=(const _CharT*) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/basic_string.h:504: note:                 std::basic_string<_CharT, _Traits, _Alloc>& std::basic_string<_CharT, _Traits, _Alloc>::operator=(_CharT) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]
movie.cpp: At global scope:
movie.cpp:240: error: variable or field ‘addLastName’ declared void
movie.cpp:240: error: ‘int Movie::addLastName’ is not a static member of ‘class Movie’
movie.cpp:240: error: ‘string’ was not declared in this scope
movie.cpp:241: error: expected ‘,’ or ‘;’ before ‘{’ token
movie.cpp:255: error: variable or field ‘addMovieName’ declared void
movie.cpp:255: error: ‘int Movie::addMovieName’ is not a static member of ‘class Movie’
movie.cpp:255: error: ‘string’ was not declared in this scope
movie.cpp:256: error: expected ‘,’ or ‘;’ before ‘{’ token
make: *** [movie.o] Error 1

Answer 1

您没有为string指定正确的命名空间，string是std命名空间的成员。在这种情况下，您需要编写std :: string，因为我看不到“using namespace std;”在你的代码中。

取代：

string movieName,
       directorLastName,
       directorFirstName,
       directorFullName;

使用：

std::string movieName,
            directorLastName,
            directorFirstName,
            directorFullName;

Answer 2

为什么所有私有字段指针？将纯int和float s存储为字段是完全可以的。而且，您不需要在构造函数中“初始化”字符串。如果不这样做，它们的默认构造函数将自动调用（string s将为空）。为什么要填充字符串？即使你在显示时需要它，也可以在那里填充它们。

Answer 3

还没有人回答这个问题，所以我想我自己把它弄清楚就把它放在这里。基本上，我的解决方案是：

在标头和实施文件中使用using std::string。

其次，声明：

stringOne = stringTwo.resize(some_number, ' ');

...失败，因为resize()是一个void返回函数。用两个单独的陈述代替它;即：

stringOne = stringTwo;
stringOne.resize(/* blah */);

...解决了其余的错误。感谢@Jesse在评论中提到这一点。

在C ++中编译链接文件的错误

3 个答案: