Question

我无法理解为什么我的代码没有改变输出文件的结果。我尝试使用“查找”成员函数来检查不正确的运算符，但它似乎没有改变结果。我如何检查字符串是否包含我正在寻找的字符串，然后替换它？

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>

using namespace std;

void input(ifstream& inputfile, ofstream& outputfile, string& cpp);

void edit(ifstream& inputfile, ofstream& outputfile, string& line);

int main()
{
    ifstream inputfile;
    ofstream outputfile;
    string line, cpp;

    input(inputfile,outputfile,cpp);

    edit(inputfile, outputfile, line);
}

void input(ifstream& inputfile, ofstream& outputfile, string& cpp)
{
    cout << "Enter a cpp file to modify" << endl;
    cin >> cpp;
    cout << endl;

    inputfile.open(cpp.c_str());
    if (inputfile.fail())
    {
        cout << "File opening failed,did you enter your file name correctly?" << endl;
        exit(1);
    }

    outputfile.open("cpp.txt");

}

void edit(ifstream& inputfile, ofstream& outputfile, string& line)
{
    string a = "cin <<";
    string b = "cout >>";

    getline(inputfile,line);

    while (! inputfile.eof())
    {
        line.find(a);
        if (line == a)
        {
            outputfile << "cin >>";
        }
        line.find(b);
        if (line == b)
        {
            outputfile << "cout >>";
        }
        else
            outputfile << line << endl;

        getline(inputfile,line);
    }
}

Answer 1

find()在字符串中搜索指定的子字符串，然后返回其位置（如果找到），它不会修改正在搜索的字符串。您忽略了find()的返回值。试试这个：

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>

using namespace std;

void input(ifstream& inputfile, ofstream& outputfile, string& cpp);

void edit(ifstream& inputfile, ofstream& outputfile, string& line);

int main()
{
    ifstream inputfile;
    ofstream outputfile;
    string line, cpp;

    input(inputfile,outputfile,cpp);

    edit(inputfile, outputfile, line);
}

void input(ifstream& inputfile, ofstream& outputfile, string& cpp)
{
    cout << "Enter a cpp file to modify" << endl;
    cin >> cpp;
    cout << endl;

    inputfile.open(cpp.c_str());
    if (!inputfile)
    {
        cout << "Input file opening failed, did you enter your file name correctly?" << endl;
        exit(1);
    }

    outputfile.open("cpp.txt");
    if (!outputfile)
    {
        cout << "Output file opening failed" << endl;
        exit(1);
    }
}

void edit(ifstream& inputfile, ofstream& outputfile, string& line)
{
    string a = "cin <<";
    string b = "cout >>";

    while (getline(inputfile,line))
    {
        if (line.find(a) != std::string::npos)
        {
            outputfile << "cin >>";
        }
        else if (line.find(b) != std::string::npos)
        {
            outputfile << "cout >>";
        }
        else
            outputfile << line << endl;
    }
}

Answer 2

我认为你的意图是：

    if (line.find(a) != string::npos)
    {
        outputfile << "cin >>";
    }

    if (line.find(b) != string::npos)
    {
        outputfile << "cout >>";
    }

Answer 3

std::string::find()没有更改字符串被调用。它试图找到作为参数发布的字符串或字符，并返回找到的字符的位置。您所要做的就是检查返回值是否等于std::string::npos，这是一个值，表示未找到子字符串：

if (line.find(a) != std::string::npos) {
    ...
}

else if (line.find(b) != std::string::npos) {
    ...
}

此外，while (!eof())通常被视为一种糟糕的编程习惯。改为在循环参数中执行输入：

while (std::getline(inputfile, line)) {
    if (line.find(a) != std::string::npos) {
        outputfile << "cin >>";
    }

    else if (line.find(b) != std::string::npos) {
        outputfile << "cout <<";
    }

    else
        outputfile << line << std::endl;
}

str.find成员函数错误

3 个答案: