[英]ifstream doesn't read values from the file
I'm making a program that works with points and files.我正在制作一个处理点和文件的程序。 I have no warnings or errors, but it still doesn't work as it should.
我没有警告或错误,但它仍然无法正常工作。 I think the problem is with the ifstream, cause the ofstream works well and puts entered the values into the file.
我认为问题出在 ifstream 上,导致 ofstream 运行良好并将输入的值放入文件中。
The output that i get looks like this我得到的输出看起来像这样
Please enter seven (x,y) pairs:
//here the seven pairs are entered
These are your points:
//(...,...)x7 with the values
These are the points read from the file:
//and the program ends and returns 0
I hope someone can help me.我希望有一个人可以帮助我。 Here's my code.
这是我的代码。
#include <iostream>
#include "std_lib_facilities.h"
using namespace std;
struct Point{
float x;
float y;
};
istream& operator>>(istream& is, Point& p)
{
return is >> p.x >> p.y;
}
ostream& operator<<(ostream& os, Point& p)
{
return os << '(' << p.x << ',' << p.y << ')';
}
void f() {
vector<Point> original_points;
cout << "Please enter seven (x,y) pairs: " << endl;
for (Point p; original_points.size() < 7;) {
cin >> p;
original_points.push_back(p);
}
cout << endl;
cout << "These are your points: " << endl;
for (int i=0; i < 7; i++) {
cout << original_points[i] << endl;
}
string name = "mydata.txt";
ofstream ost {name};
if (!ost) error("can't open output file", name);
for (Point p : original_points) {
ost << '(' << p.x << ',' << p.y << ')' << endl;
}
ost.close();
ifstream ist{name};
if (!ist) error("can't open input file", name);
vector<Point> processed_points;
for (Point p; ist >> p;) {
processed_points.push_back(p);
}
cout << endl;
cout << "These are the points read from the file: " << endl;
for (int i=1; i <= processed_points.size(); i++) {
cout << processed_points[i] << endl;
}
}
int main()
{
f();
return 0;
}
You output brackets and a comma but you don't consume them so your first read operation will fail.您输出括号和逗号,但不使用它们,因此您的第一次读取操作将失败。 Try:
尝试:
istream& operator>>(istream& is, Point& p)
{
char open;
char close;
char comma;
is >> open >> p.x >> comma >> p.y >> close;
if (open != '(' || close != ')' || comma != ',')
{
is.setstate(std::ios_base::failbit);
}
return is;
}
Your program will also crash at the end due to going out of the bounds of the vector, you are using indexes from 1
to length
, vectors are 0-indexed so should be accessed from 0
to length-1
:由于超出向量的边界,您的程序最终也会崩溃,您使用的索引从
1
到length
,向量是 0 索引的,因此应该从0
访问到length-1
:
for (int i = 0; i < processed_points.size(); i++) {
cout << processed_points[i] << endl;
}
Or just use a range based loop:或者只使用基于范围的循环:
for (auto& point : processed_points) {
cout << point << endl;
}
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