C++ 简单的字符串替换，不复杂的代码，但产生疯狂的错误

Question

首先，感谢大家的帮助！

我得到的错误是：

0x7c812afb 处未处理的异常 Readerboard.exe 中的 (kernel32.dll)： 微软 C++ 异常： 内存位置的 std::out_of_range 0x0012f8a8..

我发现问题出在这一行：

str.replace(str.find(sought), sought.size(), replacement);

它位于这个过程中：

void DisplayMessages() {

 ifstream myReadFile;
 string str;
 static string myMessages[10];
 static int i; // of course my famous i
 static int MyPosition;
 string sought;
 string replacement;

 myReadFile.open("C:\\Documents and Settings\\agerho000\\Desktop\\cms_export_test\\outages.htm",ios::in);
 i = 0; //the start of my array
 sought = "</td>"; // value that I want to replace with nothing
 replacement.clear();

 if(!myReadFile) // is there any error?
{
    cout << "Error opening the file! Aborting…\n";
    exit(1);
}

 if (myReadFile.is_open()) 
 {
    cout << endl;
    while (!myReadFile.eof()) 
    {
    getline(myReadFile, str);

    if (str == "<tr>")
    {       
        myReadFile.seekg(4,ios::cur);
        getline(myReadFile, str);
        str.replace(str.find(sought), sought.size(), replacement); 

        cout << str;

        myMessages[i]=str;
        i++;
    }

    }

}

i=0;
while (i < 10)
{
    cout << i << ") " << myMessages[i] << endl;
    i++;
        if (myMessages[i]=="")
        {
            break;
        }
} 

myReadFile.close();

mainMenu();
}

整个cpp文件如下所示：

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

using namespace std;

void mainMenu();
void DisplayMessages();
void AddMessage();
void DeleteMessage();
void EditMessage();
void RunTests();
void CheckFile();
void CreateHtmlFile(string myMessages[10]);
/*
#define MIN     1
#define MAX     100

#define TRUE    1
#define FALSE   0
*/

int main() {
    cout << endl;
    cout << endl;
    cout << "Hello Andrew.\n";
    cout << "First you need some sort of menu.\n";

    mainMenu();

    return 0;
}


void mainMenu() {

    int Command;

    cout << endl;
    cout << endl;
    cout << endl;
    cout << "What would you like to do?\n";
//  cout << "1) Check that tests work!\n";
//  cout << "2) Check that the file exists\n";
    cout << "3) Display Messages\n";
//  cout << "4) Edit a message\n";
//  cout << "5) Add a message\n";
//  cout << "6) Delete a message\n";
    cout << "7) Exit\n";
    cout << "Enter a number: ";
    cin >> Command;

    if (Command == 3)
    {
        DisplayMessages();
    }

    if (Command == 7)
    {
        cout << "Exiting...";
        exit(EXIT_SUCCESS);
    }

    if (Command == 6)
    {
        DisplayMessages();
    }
}


void DisplayMessages() {

 ifstream myReadFile;
 string str;
 static string myMessages[10];
 static int i; // of course my famous i
 static int MyPosition;
 string sought;
 string replacement;

 myReadFile.open("C:\\Documents and Settings\\agerho000\\Desktop\\cms_export_test\\outages.htm",ios::in);
 i = 0; //the start of my array
 sought = "</td>"; // value that I want to replace with nothing
 replacement.clear();

 if(!myReadFile) // is there any error?
{
    cout << "Error opening the file! Aborting…\n";
    exit(1);
}

 if (myReadFile.is_open()) 
 {
    cout << endl;
    while (!myReadFile.eof()) 
    {
    getline(myReadFile, str);

    if (str == "<tr>")
    {       
        myReadFile.seekg(4,ios::cur);
        getline(myReadFile, str);
        str.replace(str.find(sought), sought.size(), replacement); 

        cout << str;

        myMessages[i]=str;
        i++;
    }

    }

}

i=0;
while (i < 10)
{
    cout << i << ") " << myMessages[i] << endl;
    i++;
        if (myMessages[i]=="")
        {
            break;
        }
} 

myReadFile.close();

mainMenu();
}

void AddMessage() {
}
/*
void DeleteMessage() {
 ifstream myReadFile;
 string str;
 static string myMessages[10];
 static int i; // of course my famous i
 static int MyPosition;
 string sought;
 string replacement;
 static int Command;

 myReadFile.open("C:\\Documents and Settings\\agerho000\\Desktop\\cms_export_test\\outages.htm",ios::in);
 i = 0; //the start of my array
 sought = "</b></td>"; // value that I want to replace with nothing
 replacement.clear();

 if(!myReadFile) // is there any error?
{
    cout << "Error opening the file! Aborting…\n";
    exit(1);
}

 if (myReadFile.is_open()) 
 {
    cout << endl;

    while (!myReadFile.eof()) 
    {
        getline(myReadFile, str);

        if (str == "<tr>")
        {       
            myReadFile.seekg(7,ios::cur);
            getline(myReadFile, str);
            str.replace(str.find(sought), sought.size(), replacement); 

            myMessages[i]=str;
            i++;
        }

    }

}

i=0;
while (i < 10)
{
    cout << i << ") " << myMessages[i] << endl;
    i++;
        if (myMessages[i]=="")
        {
            break;
        }
} 
myReadFile.close();

cout << "Enter the number of the message you would like to delete?\n";
cout << "Or enter 11 to go back to the main menu.\n";
cin >> Command;

while (Command >= 12)
{
    cout << "Invalid number, try again!\n";
    cout << endl;
    cout << "Enter the number of the message you would like to delete?\n";
    cout << "Or enter 11 to go back to the main menu.\n";
    cin >> Command;
}

if (Command == 11)
{
    mainMenu();
}

myMessages[Command].clear();
//clear the string
//now rebuild the htm file with the new array
CreateHtmlFile(myMessages);
}

void EditMessage() {
}

void RunTests() {
}

void CheckFile() {
}

void CreateHtmlFile(string myMessages[])
{
}

                    //File.seekg(-5); moves the inside pointer 5 characters back
                    //File.seekg(40); moves the inside pointer 40 characters forward
                    //tellg() Returns an int type, that shows the current position of the inside-pointer for reading
                    //tellp() same as above but for writing
                    //seekp() just like seekg() but for writing
*/

请帮帮我！

Answer 1

一个完整的字符串替换函数：

std::string ReplaceString(std::string subject, const std::string& search,
                          const std::string& replace) {
    size_t pos = 0;
    while ((pos = subject.find(search, pos)) != std::string::npos) {
         subject.replace(pos, search.length(), replace);
         pos += replace.length();
    }
    return subject;
}

如果你需要性能，这里有一个优化的函数，它修改输入字符串，它不会创建字符串的副本：

void ReplaceStringInPlace(std::string& subject, const std::string& search,
                          const std::string& replace) {
    size_t pos = 0;
    while ((pos = subject.find(search, pos)) != std::string::npos) {
         subject.replace(pos, search.length(), replace);
         pos += replace.length();
    }
}

测试：

std::string input = "abc abc def";
std::cout << "Input string: " << input << std::endl;

std::cout << "ReplaceString() return value: " 
          << ReplaceString(input, "bc", "!!") << std::endl;
std::cout << "ReplaceString() input string not modified: " 
          << input << std::endl;

ReplaceStringInPlace(input, "bc", "??");
std::cout << "ReplaceStringInPlace() input string modified: " 
          << input << std::endl;

输出：

Input string: abc abc def
ReplaceString() return value: a!! a!! def
ReplaceString() input string not modified: abc abc def
ReplaceStringInPlace() input string modified: a?? a?? def

Answer 2

str.replace(str.find(sought), sought.size(), replacement); 是错误的，当str.find() 没有找到它正在寻找的东西时。 str.find() 将返回 str::npos，这将不是字符串中的有效位置。因此，替换调用失败，您看到的索引超出范围异常。

将其更改为：

std::size_t foundIndex = str.find(sought);
if (foundIndex != str.npos)
    str.replace(foundIndex, sought.size(), replacement);
else
    std::cout << "Oops.. didn't find " << sought << std::endl;

如果这对您有帮助，请告诉我们。

编辑：您可能还想考虑使用Boost String Algorithms Library 中的boost::algorithm::replace_all