[英]Segmentation fault reading file
#include <iostream>
#include <vector>
#include <fstream>
using namespace std;
struct Point
{
double x;
double y;
};
istream& operator>>(istream& is, Point& p)
{
char ch;
if(is >> ch && ch != '(')
{
is.unget();
is.clear(ios_base::failbit);
return is;
}
char ch2;
double x;
double y;
is >> x >> ch >> y >> ch2;
if(!is || ch != ';' || ch2 != ')')
{
cerr << "Error: Bad record!\n";
exit(1);
}
p.x = x;
p.y = y;
}
ostream& operator<<(ostream& os, const Point& p)
{
return os << '(' << p.x
<< ';' << p.y << ')' << endl;
}
int main()
{
Point p;
vector<Point> original_points;
cout << "Please enter 3 points:\n";
for(int i = 0; i < 3; ++i)
{
cin >> p;
original_points.push_back(p);
}
cout << "\nYou've entered:\n";
for(Point x : original_points)
cout << x;
ofstream ost{"mydata"};
for(Point x : original_points)
ost << x;
ost.close();
vector<Point> processed_points;
ifstream ist{"mydata"};
while(ist >> p)
processed_points.push_back(p);
ist.close();
cout << "original_points: ";
for(Point x : original_points)
cout << x;
cout << "processed_points: ";
for(Point x : original_points)
cout << x;
if(original_points.size() != processed_points.size())
cout << "Oops! Seems like something went wrong!\n";
return 0;
}
調試之后,我發現錯誤是由以下代碼行引起的:
while(ist >> p)
這部分代碼幾乎是從書本中復制的:
istream& operator>>(istream& is, Point& p)
{
char ch;
if(is >> ch && ch != '(')
{
is.unget();
is.clear(ios_base::failbit);
return is;
}
char ch2;
double x;
double y;
is >> x >> ch >> y >> ch2;
if(!is || ch != ';' || ch2 != ')')
{
cerr << "Error: Bad record!\n";
exit(1);
}
p.x = x;
p.y = y;
}
Google和stackoverflow表示此錯誤是由於錯誤地訪問內存引起的。 我花了一個小時檢查此代碼,但無法弄清楚是什么原因引起的。 我今天開始研究流,這是“編程-使用C ++的原理和實踐(第二版)”第10章的練習。
PS對不起,我的英語語法,這不是我的母語)
並不是函數operator>>(istream& is, Point& p)
中的代碼的所有分支都導致返回最終值,所以我想您忘記了推返回值return is;
在功能結束時
istream& operator>>(istream& is, Point& p)
{
char ch;
if(is >> ch && ch != '(')
{
is.unget();
is.clear(ios_base::failbit);
return is;
}
char ch2;
double x;
double y;
is >> x >> ch >> y >> ch2;
if(!is || ch != ';' || ch2 != ')')
{
cerr << "Error: Bad record!\n";
exit(1);
}
p.x = x;
p.y = y;
return is;
}
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