C++ Primer 第 9 章无法编译 : `useConvs.cc:50:19: error: call of overloaded ‘stod(std::string&)’ is ambiguous`

Question

我买了 C++ Primer 第 5 版并下载了 the accompanying zip file with sources 。该 zip 文件是为 GCC 版本 4.7.0 开发的

我在 Linux、Ubuntu 13.10 和 GCC 版本 4.8.1 上

作为对我的系统设置和下载内容的完整性检查，我尝试通过在解压 zip 文件的文件夹中键入 make 来编译示例。除第 9 章 外，所有示例均已编译。我检查了 zip 存档中的 CompilerNotes.pdf，但它没有提到这个特定的错误消息。

我的问题是

我怎样才能修复 zip 文件中的第 9 章源代码，使代码按预期编译并且代码仍然合理地与本书保持一致？

编译错误是:

g++ -std=c++0x -I.. -I..\7 -c useConvs.cc -o useConvs.o
useConvs.cc: In function ‘int main()’:
useConvs.cc:50:19: error: call of overloaded ‘stod(std::string&)’ is ambiguous
  double d = stod(s);   // converts the string s to floating-point
                   ^
useConvs.cc:50:19: note: candidates are:
In file included from useConvs.cc:33:0:
../Version_test.h:86:8: note: double stod(const string&, std::size_t*)
 double stod(const std::string &s, std::size_t * = 0)
        ^
In file included from /usr/include/c++/4.8/string:52:0,
                 from /usr/include/c++/4.8/bits/locale_classes.h:40,
                 from /usr/include/c++/4.8/bits/ios_base.h:41,
                 from /usr/include/c++/4.8/ios:42,
                 from /usr/include/c++/4.8/ostream:38,
                 from /usr/include/c++/4.8/iostream:39,
                 from ../Version_test.h:70,
                 from useConvs.cc:33:
/usr/include/c++/4.8/bits/basic_string.h:2853:3: note: double std::stod(const string&, std::size_t*)

第 55 行重复同样的错误。第 50 行显示:

        double d = stod(s);   // converts the string s to floating-point

源码:

/*
 * This file contains code from "C++ Primer, Fifth Edition", by Stanley B.
 * Lippman, Josee Lajoie, and Barbara E. Moo, and is covered under the
 * copyright and warranty notices given in that book:
 * 
 * "Copyright (c) 2013 by Objectwrite, Inc., Josee Lajoie, and Barbara E. Moo."
 * 
 * 
 * "The authors and publisher have taken care in the preparation of this book,
 * but make no expressed or implied warranty of any kind and assume no
 * responsibility for errors or omissions. No liability is assumed for
 * incidental or consequential damages in connection with or arising out of the
 * use of the information or programs contained herein."
 * 
 * Permission is granted for this code to be used for educational purposes in
 * association with the book, given proper citation if and when posted or
 * reproduced.Any commercial use of this code requires the explicit written
 * permission of the publisher, Addison-Wesley Professional, a division of
 * Pearson Education, Inc. Send your request for permission, stating clearly
 * what code you would like to use, and in what specific way, to the following
 * address: 
 * 
 *      Pearson Education, Inc.
 *      Rights and Permissions Department
 *      One Lake Street
 *      Upper Saddle River, NJ  07458
 *      Fax: (201) 236-3290
*/ 

// Version_test.h contains definitions for to_string and stod
// if the compiler does not yet define these functions,
// this code will use the definitions we provide
#include "Version_test.h" 

#include <string>
using std::string;
#ifdef STRING_NUMERIC_CONVS
using std::to_string; using std::stod;
#endif

#include <iostream>
using std::cout; using std::endl;

int main()
{
        int i = 42;
        // converts the int i to its character representation
        string s = to_string(i);  

        double d = stod(s);   // converts the string s to floating-point
        cout << "i = " << i << " s = " << s << " d is: " << d << endl;

        // convert the first substring in s that starts with a digit,  d = 3.14
        string s2 = "pi = 3.14";
        d = stod(s2.substr(s2.find_first_of("+-.0123456789")));

        cout << "d = " << d << " s = " << s << " s2 is: " << s2 << endl;

        return 0;
}

Answer 1

// Version_test.h contains definitions for to_string and stod
// if the compiler does not yet define these functions,
// this code will use the definitions we provide
#include "Version_test.h" 

有问题的代码假定编译器没有这些函数的定义，并在该 header 中提供了它自己的定义。但似乎在您的特定情况下，编译器确实提供了该功能，并且它与 zip 中提供的功能冲突。

非限定查找找到::strod，ADL 找到::std::strod，具有完全相同的签名，编译器无法确定更好的重载解析候选者。我的猜测是，简单的解决方案是删除该 header ，或者如果您的实现不提供 to_string 然后注释掉 strod