1>TestString.cpp
1>TestString.cpp(22) : error C2784: “Ning::String<CharT> Ning::operator +(const Ning::String<CharT> &,const Ning::String<CharT> &)”: 无法从“重载函数类型”为“const Ning::String<CharT> &”推导 <未知> 参数
1> String.hpp(9) : 参见“Ning::operator +”的声明
1>TestString.cpp(22) : error C2676: 二进制“+”: “string”不定义该运算符或到预定义运算符可接收的类型的转换
以下是String.hpp的内容：
#include <cstring>
namespace Ning
{
template< typename CharT >
class String;
template< typename CharT >
String<CharT> operator+(const String<CharT>& s1, const String<CharT>& s2);
/// 字符串类
template< typename CharT >
class String
{
public:
typedef unsigned size_type;
/// \brief 构造函数
String(const CharT* s = 0, size_type len = 0);
/// \brief 复制构造函数
String(const String& other);
/// \brief 重载赋值操作符
String& operator=(const String& other);
/// \brief 设定字符串内容
void assign(const CharT* s);
void assign(const CharT* s, size_type len);
void assign(const String& other);
/// \brief 清空字符串
void clear();
/// \brief 析构函数
~String();
//============================================================
/// \brief 获取字符串长度
size_type size() const { return m_len; }
/// \brief 返回内部 C 字符串指针
const CharT* c_str() const;
/// \brief 字符串是否为空
bool empty() const { return m_len == 0; }
//============================================================
/// \brief 字符串连接操作符
friend String operator+ <CharT>(const String& s1, const String& s2);
private:
CharT* m_str;
size_type m_len;
};
//////////////////////////////////////////////////////////////////////////
template< typename CharT >
struct StrTypeTrait
{
static typename String< CharT >::size_type len(const CharT* s);
static int cmp(const CharT* s1, const CharT* s2);
};
template<>
struct StrTypeTrait< char >
{
static String< char >::size_type len(const char* s) {
return strlen( s );
}
static int cmp(const char* s1, const char* s2) {
return strcmp( s1, s2 );
}
};
template< typename CharT >
Ning::String<CharT>::~String()
{
clear();
}
//////////////////////////////////////////////////////////////////////////
template< typename CharT >
Ning::String<CharT>::String(const CharT* s, size_type len)
: m_str( 0 ), m_len( len )
{
assign( s, len );
}
template< typename CharT >
Ning::String<CharT>::String(const String& other)
: m_str( 0 ), m_len( 0 )
{
assign( other );
}
template< typename CharT >
String<CharT>& Ning::String<CharT>::operator=(const String<CharT>& other)
{
assign( other );
return *this;
}
template< typename CharT >
void Ning::String<CharT>::assign(const CharT* s)
{
assign( s, 0 );
}
template< typename CharT >
void Ning::String<CharT>::assign(const CharT* s, size_type len)
{
if( s )
{
if( len == 0 )
len = StrTypeTrait< CharT >::len( s );
if( len > 0 )
{
m_str = new CharT[len + 1];
memcpy( m_str, s, len );
}
m_str[len] = 0;
//============================================================
m_len = len;
}
}
template< typename CharT >
void Ning::String<CharT>::assign(const String& other)
{
if( &other != this )
{
clear();
assign( other.m_str, other.m_len );
}
}
template< typename CharT >
void Ning::String<CharT>::clear()
{
if( m_str )
{
delete [] m_str;
m_str = 0;
}
}
template< typename CharT >
const CharT* Ning::String<CharT>::c_str() const
{
const static CharT ch = 0;
return m_str ? m_str : &ch;
}
//////////////////////////////////////////////////////////////////////////
template< typename CharT >
String<CharT> operator+(const String<CharT>& s1, const String<CharT>& s2)
{
String<CharT> ret;
if( !s1.empty() || !s2.empty() )
{
ret.m_len = s1.size() + s2.size();
ret.m_str = new CharT[ret.m_len + 1];
if( !s1.empty() )
memcpy( ret.m_str, s1.m_str, s1.size() );
if( !s2.empty() )
memcpy( ret.m_str + s1.size(), s2.m_str, s2.size() );
ret.m_str[ret.m_len] = 0;
}
return ret;
}
}
TestString.cpp的内容：
#include "String.hpp"
#include <cstdio>
typedef Ning::String< char > string;
void Print(const string& s)
{
printf( "%s[Length: %d]\n", s.c_str(), s.size() );
}
int main()
{
string s1( "Hello" );
string s2 = s1;
Print( s2 );
string s3;
Print( s3 );
s3.assign( "World!" );
string s4 = s1 + " " + s3; // 这里不能连加！！
Print( s4 );
return 0;
}
