Question

我有一个文本文件，其中包含许多行，如下所示：

%% reason of the selling ?
%% they piggy-back on cingular 's service .
zone[-3] %% also , their t-zones ."
customer service[-2] %% since i received the phone.
%% 24 hours ?"
screen[-2] %% i must have heard this about a dozen times over the span"

我想删除以%%开头的所有行，并且还有一些行在中间包含%%，所以删除%%直到该行的末尾。我想要这样的最终结果

zone[-3]
customer service[-2]
screen[-2]

Answer 1

逐行读取临时字符串。检查前两个字符是否不等于"%%"并将该字符串插入另一个文件中：

#include <iostream>
#include <fstream>
#include <string>
int main(){
    std::ifstream ifs("input.txt");
    std::ofstream ofs("output.txt");
    std::string tempstr;
    while (std::getline(ifs, tempstr)){
        if (tempstr.substr(0, 2) != "%%"){
            ofs << tempstr << std::endl;
        }
    }
}

如果您想在任何位置跳过"%%"行，请将上述if语句修改为：

if (tempstr.find("%%") == std::string::npos)

Answer 2

您没有'删除'行，但是您创建了没有这些行的副本。

对于小文件，您可以在内存中执行此操作。但是，对于大文件，您可以创建新文件，删除旧文件，并重命名新文件以匹配旧文件。

{{1}}

对于删除/重命名部分，请查看How to change a text file's name in C++

Answer 3

您要覆盖旧文件，还是只想获取过滤后的数据？在过滤的情况下，我不会使用专门的解决方案，只是常见的拆分函数第一个结果。

#include <string>

//surely you have your own splitting function, this is just an example
std::vector<std::string> stringSplit(std::string s, std::string delim, int start/*=0*/)
{
    std::vector<std::string> result;
    std::string s1 = s + delim; //to find at least one
    auto delimPos = s1.find(delim, start), 
        delimLen = delim.length(),
        pMax = s1.length(), tokenLen = delimPos - start,
        startPos = delimPos - tokenLen;
    while (((int)delimPos > -1) && (delimPos < pMax) )
    {
        tokenLen = delimPos - startPos;
        result.push_back(s1.substr(startPos, tokenLen));
        startPos = delimPos + delimLen;
        delimPos = s1.find(delim, startPos);
    }
    return(result);
}


std::vector<std::string> lines = {
        "%% reason of the selling ?",
        "zone[-3] %% also , their t-zones .",
        "customer service[-2] ## since i received the phone.",
        "customer service[-2] %% since i received the phone.",
        "%% 24 hours ?\"",
        "screen[-2] %% i must have heard this about a dozen times over the span\"" };
std::string result;
for (auto line : lines)
{
    result = (stringSplit(line, "%%"))[0];
    if (result != "")
        std::cout << result << std::endl;
}

输出：

zone[-3]
customer service[-2] ## since i received the phone.
customer service[-2]
screen[-2]

我想删除以%%（C ++）开头的txt文件中的一些行

3 个答案: