C++ 在文本文件中搜索特定字符串并返回该字符串所在的行号

2022-01-19 00:00:00 return search c++

c++ 中是否有特定的函数可以返回我要查找的特定字符串的行号?

Is there a particular function in c++ that can return the line number of a particular string i want to find?

ifstream fileInput;
int offset;
string line;
char* search = "a"; // test variable to search in file
// open file to search
fileInput.open(cfilename.c_str());
if(fileInput.is_open()) {
    while(!fileInput.eof()) {
        getline(fileInput, line);
        if ((offset = line.find(search, 0)) != string::npos) {
            cout << "found: " << search << endl;
        }
    }
    fileInput.close();
}
else cout << "Unable to open file.";

我想在以下位置添加一些代码:

I want to add some codes at:

    cout << "found: " << search << endl;

这将返回行号，后跟搜索的字符串.

That will return the line number followed by the string that was searched.

推荐答案

只需使用计数器变量来跟踪当前行号.每次您调用 getline 时，您...读取一行...所以在那之后增加变量.

Just use a counter variable to keep track of the current line number. Each time you call getline you... read a line... so just increment the variable after that. 

unsigned int curLine = 0;
while(getline(fileInput, line)) { // I changed this, see below
    curLine++;
    if (line.find(search, 0) != string::npos) {
        cout << "found: " << search << "line: " << curLine << endl;
    }
}

还有……

while(!fileInput.eof())

应该是

while(getline(fileInput, line))

如果读取时发生错误 eof 将不会被设置，所以你有一个无限循环.std::getline 返回一个流(你传递给它的流)，它可以隐式转换为 bool，它告诉你是否可以继续阅读，而不仅仅是如果你在文件的末尾.

If an error occurs while reading eof will not be set, so you have an infinite loop. std::getline returns a stream (the stream you passed it) which can be implicitly converted to a bool, which tells you if you can continue to read, not only if you are at the end of the file.

如果设置了eof，你仍然会退出循环，但是如果设置了bad，你也会退出，当你阅读时有人删除了文件它等等.

If eof is set you will still exit the loop, but you will also exit if, for example, bad is set, someone deletes the file while you are reading it, etc.

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