Question

我正在尝试编写自己的字符串类（用于理解目的）。我写的如下， file 1 string.h

#include<iostream>
#include<string.h>
namespace MyString
{
class string
{
char* ch;
int len;
public:
string();
string(const char* ch);
char* getString();
int length();
};
}

file 2 string.cpp

#include<iostream>
#include"string.h"
using namespace std;
using MyString::string; // use string from MyString namespace only.
string::string()
{                       
ch = NULL;      
len = 0;
}                     
string::string(const char* ch)
{                       
this->ch = ch;  
}   
char* string::getString()
{
return ch;
}
int string::length()
{
return len;
}
int main()
{
string obj = "This is a test";
cout << obj.getstring<<endl;
return 0;
}

但我的程序甚至无法编译，并出现以下错误

g++     string.cpp   -o string
string.cpp:6:1: error: reference to ‘string’ is ambiguous
string.h:5:8: error: candidates are: class MyString::string
/usr/include/c++/4.6/bits/stringfwd.h:65:33: error:                 typedef struct std::basic_string<char> std::string
string.cpp:6:1: error: ‘string’ does not name a type
string.cpp:12:1: error: reference to ‘string’ is ambiguous
string.h:5:8: error: candidates are: class MyString::string
/usr/include/c++/4.6/bits/stringfwd.h:65:33: error:                 typedef struct std::basic_string<char> std::string
string.cpp:12:1: error: ‘string’ does not name a type
string.cpp:23:7: error: reference to ‘string’ is ambiguous
string.h:5:8: error: candidates are: class MyString::string
/usr/include/c++/4.6/bits/stringfwd.h:65:33: error:                 typedef struct std::basic_string<char> std::string
string.cpp:23:7: error: reference to ‘string’ is ambiguous
string.h:5:8: error: candidates are: class MyString::string
/usr/include/c++/4.6/bits/stringfwd.h:65:33: error:                 typedef struct std::basic_string<char> std::string
string.cpp: In function ‘char* getString()’:
string.cpp:25:9: error: ‘ch’ was not declared in this scope
string.cpp: At global scope:
string.cpp:28:5: error: reference to ‘string’ is ambiguous
string.h:5:8: error: candidates are: class MyString::string
/usr/include/c++/4.6/bits/stringfwd.h:65:33: error:                 typedef struct std::basic_string<char> std::string
string.cpp:28:5: error: reference to ‘string’ is ambiguous
string.h:5:8: error: candidates are: class MyString::string
/usr/include/c++/4.6/bits/stringfwd.h:65:33: error:                 typedef struct std::basic_string<char> std::string
string.cpp: In function ‘int length()’:
string.cpp:30:9: error: ‘len’ was not declared in this scope
string.cpp: In function ‘int main()’:
string.cpp:35:2: error: reference to ‘string’ is ambiguous
string.h:5:8: error: candidates are: class MyString::string
/usr/include/c++/4.6/bits/stringfwd.h:65:33: error:                 typedef struct std::basic_string<char> std::string
string.cpp:35:9: error: expected ‘;’ before ‘obj’
make: *** [string] Error 1

我没有得到共鸣，为什么编译器在显式使用MyNamespace中的字符串时出错（即使用MyNamespace :: string;）？这方面的任何指示都会非常有用。

Answer 1

您的cpp文件中是using namespace std。现在std中有一个字符串，MySpace中有一个字符串，因此编译器不知道选择哪一个。使用限定名称来区分它们，例如MyString::string而不是string或删除using namespace std;或将整个实现放入namespace MyString { ... }。

Answer 2

您的<string.h>包含string标识符，并且您使用MyClass声明将using引入全局命名空间。这导致名称冲突。

只需删除<string.h>文件（无论如何你似乎都没有使用它）。

Answer 3

命名空间是该问题的解决方案但是，ai建议始终保持所有签名的显式。

   using namespace std;

是一个很好的捷径，如果你必须混合不同的lib，包含字符串，矢量等，即STL + BOOST

，它将变得一团糟

删除using子句，并在每个STL对象上添加std ::。

编写我自己的字符串类，但获取“引用'字符串'是不明确的”编译错误

file 2 string.cpp

3 个答案: