ifstream文件在从行中读取时被清除

Ifstream file getting cleared when reading from line

本文关键字：读取 清除 文件 ifstream      更新时间：2023-10-16

我正在尝试从C++的输入纺织品中读取用空格分隔的字符。我已经成功打开了该文件并能够循环访问它。但是，每当我尝试从文件中的字符中分配变量时，这些行似乎都被清除了。第一行的变量设置正确，但不在第一行之后。我不确定我是否错误地访问了文件，是否缺少一个标志，或者是否有更好的方法来访问字符。

法典：

int lineNumber = 0,*linesMaxVal = new int[lineCount];
string line;
while (getline(infile, line)) {
cout << "line # is " << lineNumber << " line val is: " << "'" << line << "'" << endl;
int x1,x2,x3,x4,x5,max;
infile >> x1 >> x2 >> x3 >> x4 >> x5;
}

如果行"infile>> x1>> x2>> x3 ...等"被删除，输出如下(正确(

line # is 0 line val is: '0 0 0 0 0'
line # is 0 line val is: '1 2 3 4 5'
line # is 0 line val is: '5 4 3 2 1'
line # is 0 line val is: '5 100 1000 10000 10500'
line # is 0 line val is: '99999 99999 99998 99999 99999'
line # is 0 line val is: '-1 0 0 0 -1'
line # is 0 line val is: '-9999 -9999 -9998 -9999 -9999'
line # is 0 line val is: '50 1234 457 789 7'
line # is 0 line val is: '123240 -124 -453 234 -99999'
line # is 0 line val is: '234 235 -109 0 12'
line # is 0 line val is: '777 987 234 345 111'
line # is 0 line val is: '12 0 -19 27 19'
line # is 0 line val is: '0 0 0 0 0'
line # is 0 line val is: '-99 -900 45 20 10'
line # is 0 line val is: '13 -56 99 123 90'
line # is 0 line val is: '0 0 1 -11 -1'
line # is 0 line val is: ''

否则，如果保留 infile 行并定义了变量，则输出如下所示。

line # is 0 line val is: '0 0 0 0 0'
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''
line # is 0 line val is: ''

任何帮助不胜感激！

infile >> x1 >> x2 >> x3 >> x4 >> x5;

读取行上的所有数字，但在流中保留换行符。

然后你回到循环的头部并运行：

getline(infile, line)

它立即看到一个换行符，所以它给你一个空字符串，吃掉换行符并继续前进。

这里最大的问题是提取运算符(>>(在流中留下了它停止的空格(在本例中为换行符(，而getline吃掉它停止的任何分量。将两者混合会导致这样的小打嗝。

一种可能的解决方法是在提取运算符之后添加一个ignore，以将换行符从流中取出。

在聊天中进行了一些讨论之后，看起来您想遍历文件并找到每行的最大值。我建议使用向量来存储每行的值，并使用算法库来查找最大值：

//Our temp vector. It'll hold a line worth of ints
vector<int> line(5);
while(true) { //one loop = one line
//Loop and read 5 ints (one line's worth) into the vector 
for(int x = 0; x < 5 && infile >> line.at(x); x++) { }
if(!infile) { break; } //if we read through everything, we're done!
//find the biggest value in the vector
int biggest = *max_element(line.begin(), line.end());
//Do some things with it...
cout << "Biggest is: " << biggest << endl;
}

有关工作演示，请参见此处： ideone

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