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学习Essential C++例题时遇到的问题

时间：2010-09-10

来源：互联网

本帖最后由 showboy 于 2010-09-10 05:18 编辑

Essential C++这本书估计大家都知道吧,不知道的可以看这里
http://book.douban.com/subject/1215826/

在练习题2.5和2.6中遇到一问题,不求甚解,请指教,谢谢

编译环境是Code::Block 8.02
其自带的GCC为 gcc-g++-3.4.5-20060117-1-vista.tar.gz

以下是2.5中的源码,可以正确编译,问题在后面的2.6中

练习2.5的源码

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using std::cin;
using std::cout;
using std::endl;
using std::vector;
using std::string;
using std::max_element;
inline int max(int t1,int t2){
return t1>t2? t1:t2;
}
inline float max(float t1,float t2){
return t1>t2? t1:t2;
}
inline string max(const string &t1,const string &t2){
return t1>t2? t1:t2;
}
//////////////////////////////////////////////////////////////
inline int max(const vector<int> &vec){
return *max_element(vec.begin(),vec.end());
}
inline float max(const vector<float> &vec){
return *max_element(vec.begin(),vec.end());
}
inline string max(const vector<string> &vec){
return *max_element(vec.begin(),vec.end());
}
////////////////////////////////////////////////////////////
inline int max(const int *parray,int size){
return *max_element(parray,parray+size);
}
inline float max(const float *parray,int size){
return *max_element(parray,parray+size);
}
inline string max(const string *parray,int size){
return *max_element(parray,parray+size);
}
int main()
{
string sarray[]={"we","were","her","pride","of","ten"};
vector<string> svec(sarray,sarray+6);
int iarray[]={12,70,2,169,1,5,29};
vector<int>ivec(iarray,iarray+7);
float farray[]={2.5,24.8,18.7,4.1,23.9};
vector<float>fvec(farray,farray+5);
int imax=max(max(ivec),max(iarray,7));
float fmax=max(max(fvec),max(farray,5));
string smax=max(max(svec),max(sarray,6));
cout<<"imax should be 169 --found:"<<imax<<endl;
cout<<"imax should be 24.8 --found:"<<fmax<<endl;
cout<<"imax should be were --found:"<<smax<<endl<<endl;
cout<<max(ivec)<<","<<max(iarray,7)<<endl;
cout<<max(fvec)<<","<<max(farray,5)<<endl;
cout<<max(svec)<<","<<max(sarray,6)<<endl;
return true;
}

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练习2.6的源码

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using std::cin;
using std::cout;
using std::endl;
using std::vector;
using std::string;
using std::max_element;
template <typename Type> inline Type max(Type t1,Type t2){
return t1>t2? t1:t2;
}
template <typename elemType> inline elemType max(const vector<elemType> &vec){
return *max_element(vec.begin(),vec.end());
}
template <typename arrayType> inline arrayType max(const arrayType *parray,int size){
return *max_element(parray,parray+size);
}
int main()
{
string sarray[]={"we","were","her","pride","of","ten"};
vector<string> svec(sarray,sarray+6);
int iarray[]={12,70,2,169,1,5,29};
vector<int>ivec(iarray,iarray+7);
float farray[]={2.5,24.8,18.7,4.1,23.9};
vector<float>fvec(farray,farray+5);
int imax=max(max(ivec),max(iarray,7));
float fmax=max(max(fvec),max(farray,5));
string smax=max(max(svec),max(sarray,6));
cout<<"imax should be 169 --found:"<<imax<<endl;
cout<<"imax should be 24.8 --found:"<<fmax<<endl;
cout<<"imax should be were --found:"<<smax<<endl<<endl;
cout<<max(ivec)<<","<<max(iarray,7)<<endl;
cout<<max(fvec)<<","<<max(farray,5)<<endl;
cout<<max(svec)<<","<<max(sarray,6)<<endl;
return true;
}

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编译练习2.6的错误信息如下

D:\MY_CPLUSPLUS\essential_C++\2.6.cpp||In function `int main()':|
D:\MY_CPLUSPLUS\essential_C++\2.6.cpp|38|error: call of overloaded `max(std::string, std::string)' is ambiguous|
D:\MY_CPLUSPLUS\essential_C++\2.6.cpp|13|note: candidates are: Type max(Type, Type) [with Type = std::basic_string<char, std::char_traits<char>, std::allocator<char> >]|
D:\Program Files\CodeBlocks\MinGW\bin\..\lib\gcc\mingw32\3.4.5\..\..\..\..\include\c++\3.4.5\bits\stl_algobase.h|173|note: const _Tp& std::max(const _Tp&, const _Tp&) [with _Tp = std::string]|
||=== Build finished: 1 errors, 0 warnings ===|

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用DEV C++也是差不多的错误,

怀疑其中的问题在于练习2.5中的21行的函数中存在传址(by reference)的问题,而int和float函数没用使用反应用,不知道这样理解对不对?

inline string max(const string &t1,const string &t2){
return t1>t2? t1:t2;
}

这里的&在练习2.6中会出现共用template max()函数出现问题

初学c++不知道如何解决,请指教

另外用MS VC++6.0可以编译通过,不过有不少警告,具体信息如下

d:\my_cplusplus\essential_c++\2.6.cpp(33) : warning C4305: 'initializing' : truncation from 'const double' to 'float'
d:\my_cplusplus\essential_c++\2.6.cpp(33) : warning C4305: 'initializing' : truncation from 'const double' to 'float'
d:\my_cplusplus\essential_c++\2.6.cpp(33) : warning C4305: 'initializing' : truncation from 'const double' to 'float'
d:\my_cplusplus\essential_c++\2.6.cpp(33) : warning C4305: 'initializing' : truncation from 'const double' to 'float'
d:\my_cplusplus\essential_c++\2.6.cpp(49) : warning C4786: 'std::reverse_iterator<std::basic_string<char,std::char_traits<char>,std::allocator<char> > const *,std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::basic_string<cha
r,std::char_traits<char>,std::allocator<char> > const &,std::basic_string<char,std::char_traits<char>,std::allocator<char> > const *,int>' : identifier was truncated to '255' characters in the debug information
d:\my_cplusplus\essential_c++\2.6.cpp(49) : warning C4786: 'std::reverse_iterator<std::basic_string<char,std::char_traits<char>,std::allocator<char> > *,std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::basic_string<char,std:
:char_traits<char>,std::allocator<char> > &,std::basic_string<char,std::char_traits<char>,std::allocator<char> > *,int>' : identifier was truncated to '255' characters in the debug information
d:\program files\vc6\vc98\include\vector(56) : warning C4786: 'std::vector<std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::allocator<std::basic_string<char,std::char_traits<char>,std::allocator<char> > > >::vector<std::basi
c_string<char,std::char_traits<char>,std::allocator<char> >,std::allocator<std::basic_string<char,std::char_traits<char>,std::allocator<char> > > >' : identifier was truncated to '255' characters in the debug information
d:\program files\vc6\vc98\include\vector(60) : warning C4786: 'std::vector<std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::allocator<std::basic_string<char,std::char_traits<char>,std::allocator<char> > > >::~vector<std::bas
ic_string<char,std::char_traits<char>,std::allocator<char> >,std::allocator<std::basic_string<char,std::char_traits<char>,std::allocator<char> > > >' : identifier was truncated to '255' characters in the debug information
2.6.obj - 0 error(s), 0 warning(s)

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