C++入門練習1.20運行錯誤

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C++ Primer 5th Edition中的練習1.20當我運行我的程序時發生錯誤。我試過在3臺不同的計算機上運行該程序，結果相同。我一直在使用Visual Studio 2015作爲我的IDE。我懷疑Visual Studio是罪魁禍首，但我對它的瞭解還不夠多，而且我對搜索沒有任何好運。謝謝！C++入門練習1.20運行錯誤

錯誤消息如下：

調試斷言失敗！

程序：C：\ WINDOWS \ SYSTEM32 \ MSVCP140D.dll文件：C：\ Program Files文件（x86）的\微軟的Visual Studio 14.0 \ VC \ \包括線路xstring：1175

表達：無效的空指針

以下是我的源代碼：

#include <iostream> 
#include "Sales_item.h" 

    int main() 
    { 
     Sales_item nonzero = 0; 
     while (std::cin >> nonzero) 
      std::cout << nonzero; 
     return 0; 
    }

頭文件「Sales_item.h」如下：

#ifndef SALESITEM_H 
// we're here only if SALESITEM_H has not yet been defined 
#define SALESITEM_H 

#include "Version_test.h" 

// Definition of Sales_item class and related functions goes here 
#include <iostream> 
#include <string> 

class Sales_item { 
// these declarations are explained section 7.2.1, p. 270 
// and in chapter 14, pages 557, 558, 561 
friend std::istream& operator>>(std::istream&, Sales_item&); 
friend std::ostream& operator<<(std::ostream&, const Sales_item&); 
friend bool operator<(const Sales_item&, const Sales_item&); 
friend bool 
operator==(const Sales_item&, const Sales_item&); 
public: 
    // constructors are explained in section 7.1.4, pages 262 - 265 
    // default constructor needed to initialize members of built-in type 
#if defined(IN_CLASS_INITS) && defined(DEFAULT_FCNS) 
    Sales_item() = default; 
#else 
    Sales_item(): units_sold(0), revenue(0.0) { } 
#endif 
    Sales_item(const std::string &book): 
       bookNo(book), units_sold(0), revenue(0.0) { } 
    Sales_item(std::istream &is) { is >> *this; } 
public: 
    // operations on Sales_item objects 
    // member binary operator: left-hand operand bound to implicit this pointer 
    Sales_item& operator+=(const Sales_item&); 

    // operations on Sales_item objects 
    std::string isbn() const { return bookNo; } 
    double avg_price() const; 
// private members as before 
private: 
    std::string bookNo;  // implicitly initialized to the empty string 
#ifdef IN_CLASS_INITS 
    unsigned units_sold = 0; // explicitly initialized 
    double revenue = 0.0; 
#else 
    unsigned units_sold; 
    double revenue;  
#endif 
}; 

// used in chapter 10 
inline 
bool compareIsbn(const Sales_item &lhs, const Sales_item &rhs) 
{ return lhs.isbn() == rhs.isbn(); } 

// nonmember binary operator: must declare a parameter for each operand 
Sales_item operator+(const Sales_item&, const Sales_item&); 

inline bool 
operator==(const Sales_item &lhs, const Sales_item &rhs) 
{ 
    // must be made a friend of Sales_item 
    return lhs.units_sold == rhs.units_sold && 
      lhs.revenue == rhs.revenue && 
      lhs.isbn() == rhs.isbn(); 
} 

inline bool 
operator!=(const Sales_item &lhs, const Sales_item &rhs) 
{ 
    return !(lhs == rhs); // != defined in terms of operator== 
} 

// assumes that both objects refer to the same ISBN 
Sales_item& Sales_item::operator+=(const Sales_item& rhs) 
{ 
    units_sold += rhs.units_sold; 
    revenue += rhs.revenue; 
    return *this; 
} 

// assumes that both objects refer to the same ISBN 
Sales_item 
operator+(const Sales_item& lhs, const Sales_item& rhs) 
{ 
    Sales_item ret(lhs); // copy (|lhs|) into a local object that we'll return 
    ret += rhs;   // add in the contents of (|rhs|) 
    return ret;   // return (|ret|) by value 
} 

std::istream& 
operator>>(std::istream& in, Sales_item& s) 
{ 
    double price; 
    in >> s.bookNo >> s.units_sold >> price; 
    // check that the inputs succeeded 
    if (in) 
     s.revenue = s.units_sold * price; 
    else 
     s = Sales_item(); // input failed: reset object to default state 
    return in; 
} 

std::ostream& 
operator<<(std::ostream& out, const Sales_item& s) 
{ 
    out << s.isbn() << " " << s.units_sold << " " 
     << s.revenue << " " << s.avg_price(); 
    return out; 
} 

inline bool operator<(const Sales_item &, const Sales_item &) 
{ 
    return false; 
} 

double Sales_item::avg_price() const 
{ 
    if (units_sold) 
     return revenue/units_sold; 
    else 
     return 0; 
} 
#endif

它引用另一個名爲「Version_test.h」的頭文件。

#ifndef VERSION_TEST_H 
#define VERSION_TEST_H 

/* As of the first printing of C++ Primer, 5th Edition (July 2012), 
* the Microsoft Complier did not yet support a number of C++ 11 features. 
* 
* The code we distribute contains both normal C++ code and 
* workarounds for missing features. We use a series of CPP variables to 
* determine whether a given features is implemented in a given release 
* of the MS compiler. The base version we used to test the code in the book 
* is Compiler Version 17.00.50522.1 for x86. 
* 
* When new releases are available we will update this file which will 
* #define the features implmented in that release. 
*/ 

#if _MSC_FULL_VER == 170050522 || _MSC_FULL_VER == 170050727 
// base version, future releases will #define those features as they are 
// implemented by Microsoft 

/* Code in this delivery use the following variables to control compilation 

    Variable tests   C++ 11 Feature 
CONSTEXPR_VARS   constexpr variables 
CONSTEXPR_FCNS   constexpr functions 
CONSTEXPR_CTORS   constexpr constructors and other member functions 
DEFAULT_FCNS    = default 
DELETED_FCNS    = delete 
FUNC_CPP     __func__ local static 
FUNCTION_PTRMEM   function template with pointer to member function 
IN_CLASS_INITS   in class initializers 
INITIALIZER_LIST   library initializer_list<T> template 
LIST_INIT     list initialization of ordinary variables 
LROUND     lround function in cmath 
NOEXCEPT     noexcept specifier and noexcept operator 
SIZEOF_MEMBER    sizeof class_name::member_name 
TEMPLATE_FCN_DEFAULT_ARGS default template arguments for function templates 
TYPE_ALIAS_DECLS   type alias declarations 
UNION_CLASS_MEMS   unions members that have constructors or copy control 
VARIADICS     variadic templates 
*/ 
#endif // ends compiler version check 

#ifndef LROUND 
inline long lround(double d) 
{ 
    return (d >= 0) ? long(d + 0.5) : long(d - 0.5); 
} 
#endif 

#endif // ends header guard

來源

2016-02-10 Philip Jackson

作爲第一步在調試器中運行你的程序，逐行逐行找出錯誤的確切來源。 –

該程序正在建設中。問題只在我運行時才顯示。 –

你給這個程序什麼輸入？ – NathanOliver

你的問題是由這一行造成的：

Sales_item nonzero = 0;

因爲此構造：

Sales_item(const std::string &book)

這是用來因爲0可以表示一個空char*和std::string可從char*構建。

您的問題發生是因爲從空指針構造std::string無效。

該行應

Sales_item nonzero;

（順便說一句，這是極爲罕見的工具，就出現故障。最有可能的罪魁禍首是永遠是你自己寫的代碼。）

來源

2016-02-10 15:27:32 molbdnilo

C++入門練習1.20運行錯誤

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