Question

我想在WinAPI中创建2个线程，这些线程将能够写入单个文本文件。我知道如何创建文件并将其写入。

#include <iostream>
#include <windows.h>
#include <string>

DWORD WINAPI firstthred(LPVOID lpParameter) {
    // here I want one thread to write something in the txt file Something like this
    HANDLE hFile = CreateFile(
        L"C:\\Users\\Yon\\OneDrive\\Desktop\\example3.txt", FILE_WRITE_DATA, NULL, NULL, CREATE_NEW, NULL, NULL
    );
    char str[] = "Hello ";//Example text
    DWORD bytesWritten;
    WriteFile(hFile, str, strlen(str), &bytesWritten, NULL);
    DWORD myThreadID;
}

DWORD WINAPI secondthred(LPVOID lpParameter) {
    // here I want the other thread to write something different in the same txt file something like this
    HANDLE hFile = CreateFile(
        L"C:\\Users\\Yon\\OneDrive\\Desktop\\example3.txt", FILE_WRITE_DATA, NULL, NULL, CREATE_NEW, NULL, NULL
    );
    char str[] = "World"; //a diffrent Example of a text in the same file
    DWORD bytesWritten;
    WriteFile(hFile, str, strlen(str), &bytesWritten, NULL);
    DWORD myThreadID;
}

int main()
{
    HANDLE hThread = CreateThread(
        NULL,
        0,
        firstthred,
        NULL,
        0,
        &myThreadID
    );
    HANDLE hThread = CreateThread(
        NULL,
        0,
        secondthred,
        NULL,
        0,
        &myThreadID
    );
}

如何创建2个写入文本文件的线程？

Answer 1

首先，使用CREAT_NEW标志，如果指定的文件存在，则函数失败。因此，如果两个线程都在运行，则两个线程中总会有CreateFile失败，或者两个线程都失败。您可以在第一个线程中使用CREATE_ALWAYS，在第二个线程中使用OPEN_ALWAYS。

如果要在“相同时间”写入同一文件，则需要

FILE_SHARE_WRITE。但这将导致您的一个输入被另一个线程覆盖。这是因为

每次打开文件时，系统都会将文件指针放在文件的开头，偏移量为零。

除非您按以下顺序编写：

"      World"
"Hello"

所以关键是控制文件指针。在您的示例中，您只需要同步写入顺序，然后在第二次打开文件时将文件指针设置为文件末尾（SetFilePointer）（无需进行任何错误检查，统一字符集）。

#include <iostream>
#include <windows.h>
#include <string>
#include <tchar.h>
HANDLE hmutex;
DWORD WINAPI firstthred(LPVOID lpParameter) {
    // here I want one thread to write something in the txt file Something like this
    WaitForSingleObject(hmutex, INFINITE);
    HANDLE hFile = CreateFile(
        TEXT("Path\\example3.txt"), FILE_WRITE_DATA, NULL, NULL, CREATE_ALWAYS, NULL, NULL
    );
    TCHAR str[] = TEXT("Hello ");//Example text
    DWORD bytesWritten;
    WriteFile(hFile, str, _tcslen(str)*sizeof(TCHAR), &bytesWritten, NULL);
    CloseHandle(hFile);
    ReleaseMutex(hmutex);
    return 0;
}

DWORD WINAPI secondthred(LPVOID lpParameter) {
    // here I want the other thread to write something different in the same txt file something like this
    WaitForSingleObject(hmutex, INFINITE);
    HANDLE hFile = CreateFile(
        TEXT("Path\\example3.txt"), FILE_WRITE_DATA, NULL, NULL, OPEN_ALWAYS, NULL, NULL
    );
    //SetEndOfFile(hFile);
    SetFilePointer(hFile, 0, NULL, FILE_END);
    TCHAR str[] = TEXT("World"); //a diffrent Example of a text in the same file
    DWORD bytesWritten;
    WriteFile(hFile, str, _tcslen(str)*sizeof(TCHAR), &bytesWritten, NULL);
    CloseHandle(hFile);
    ReleaseMutex(hmutex);
    return 0;
}

int main()
{
    hmutex = CreateMutex(NULL, false, NULL);
    DWORD myThreadID[2] = { 0 };
    HANDLE hThread[2] = { 0 };
    hThread[0] = CreateThread(
        NULL,
        0,
        firstthred,
        NULL,
        0,
        &myThreadID[0]
    );
    hThread[1] = CreateThread(
        NULL,
        0,
        secondthred,
        NULL,
        0,
        &myThreadID[1]
    );
    WaitForMultipleObjects(2, hThread, TRUE, INFINITE);//Wait for the threads exit.
    return 0;
}

如果您真正想做的是同时在每个线程中循环写入文件，则建议您只打开一个文件句柄并将其传递给lpParameter。

如何创建2个写入文本文件的线程？

1 个答案: