c - MapViewOfFile-OpenFileMapping(需要帮助)

Question

``我正在努力做我的家庭作业，但我无法继续，需要你的帮助。我有两个使用相同文件 (log.txt) 的进程。当我尝试同时写一些东西时，它会覆盖并且只有一个进程写入 txt。

这是我的创作过程，

enter code here
     #include <Windows.h>
    #include <stdlib.h>
   #include <stdio.h>
       #include "..\\def.h"



      int main(){

HANDLE hReadPipe;
HANDLE hWritePipe;
HANDLE hMMap;
DWORD bytesWritten;
HANDLE hFile;
STARTUPINFO si_e;
PROCESS_INFORMATION pi_e;

STARTUPINFO si_d;
PROCESS_INFORMATION pi_d;


SECURITY_ATTRIBUTES sa;

sa.bInheritHandle = TRUE;
sa.lpSecurityDescriptor = NULL;
sa.nLength = sizeof(SECURITY_ATTRIBUTES);

    if(!CreatePipe(&hReadPipe,&hWritePipe, &sa,0))
    fprintf(stderr,"Unable to create pipe.\n");
ZeroMemory(&si_e, sizeof(STARTUPINFO));
ZeroMemory(&si_d, sizeof(STARTUPINFO));



if((hFile =CreateFile(  FILE_NAME,
                        GENERIC_READ|GENERIC_WRITE,
                        FILE_SHARE_READ|FILE_SHARE_WRITE,
                        NULL,
                        OPEN_ALWAYS,
                        FILE_ATTRIBUTE_NORMAL,
                        NULL)) 
                                == INVALID_HANDLE_VALUE){
    fprintf(stderr,"PARENT: Unable to open file %s: %d\n",FILE_NAME,GetLastError());
    exitPrompt();
}

if((hMMap = CreateFileMapping(      hFile,
                                NULL,
                                PAGE_READWRITE,
                                0,
                                BUFF_SIZE*2,
                                "Global\\file_log_txt")) 
                                            == NULL){
    fprintf(stderr,"PARENT: Unable to create memory mapping: %d\n",GetLastError());

}



si_e.cb = sizeof(si_e);
si_e.hStdInput = GetStdHandle(STD_INPUT_HANDLE);
si_e.hStdOutput =hWritePipe;
si_e.hStdError = GetStdHandle(STD_ERROR_HANDLE);
si_e.dwFlags = STARTF_USESTDHANDLES;

        if(!CreateProcess(  NULL,
                    "..\\Debug\\Encrypter.exe",
                    NULL,
                    NULL,
                    TRUE,
                    CREATE_NEW_CONSOLE,
                    NULL,
                    NULL,
                    &si_e,
                    &pi_e))
    fprintf(stderr,"Unable to create child process.\n");








si_d.cb = sizeof(si_d);
si_d.hStdInput= hReadPipe;
si_d.hStdOutput = GetStdHandle(STD_OUTPUT_HANDLE);
si_d.hStdError = GetStdHandle(STD_ERROR_HANDLE);
si_d.dwFlags = STARTF_USESTDHANDLES;

         if(!CreateProcess( NULL,
                    "..\\Debug\\Decrypter.exe",
                    NULL,
                    NULL,
                    TRUE,
                    CREATE_NEW_CONSOLE,
                    NULL,
                    NULL,
                    &si_d,
                    &pi_d))
    fprintf(stderr,"Unable to create child process.\n");



Sleep(5000000);
return 0;

1.流程:

enter code here
       #include <stdlib.h>
     #include <stdio.h>
      #include <Windows.h>
          #include "..\\def.h"
              int main()
       {
int i;
HANDLE writeHandle;
HANDLE hFile, hMMap;
DWORD bytesToWrite,bytesWritten,a=50;
char * pFile, *start;
char message[50][15];   
char code[]=" ";
int index;
writeHandle = GetStdHandle(STD_OUTPUT_HANDLE);

    if((hMMap = OpenFileMapping(FILE_MAP_ALL_ACCESS,FALSE,"Global\\file_log_txt")) == NULL){
    fprintf(stderr,"Unable to create memory mapping: %d\n",GetLastError());

}

if( ( pFile = (char *) MapViewOfFile(hMMap,FILE_MAP_ALL_ACCESS,0,0,BUFF_SIZE)) == NULL)
{
    fprintf(stderr,"Unable to create map view: %d\n",GetLastError());

}

    //student number =160201007(0+0+7=7)  +7encrypter
while(1){

    gets(code);
    for(  i=0;i<strlen(code);i++){
    code[i]=code[i]+7;
}
    bytesToWrite = strlen(code);
    bytesToWrite++;
    WriteFile(writeHandle,code,bytesToWrite,&bytesWritten,NULL);

}
start = pFile;
*(pFile)=*(pFile)+50;
while(pFile < start+ 100){
        *(pFile=pFile+80);
    *(pFile++) = 'A';
    break;  
}
system("pause");
return 0;
             }

2.过程:

enter code here
         #include <stdlib.h>
            #include <stdio.h>
           #include <Windows.h>
                #include "..\\def.h"
          int main()

          { 

char message[80];
int index,i;
HANDLE hFile, hMMap;
char * pFile, *start;
    if((hMMap = OpenFileMapping(FILE_MAP_ALL_ACCESS,FALSE,"Global\\file_log_txt")) == NULL){
    fprintf(stderr,"Unable to create memory mapping: %d\n",GetLastError());

}

if( ( pFile = (char *) MapViewOfFile(hMMap,FILE_MAP_ALL_ACCESS,0,0,BUFF_SIZE)) == NULL)
{
    fprintf(stderr,"Unable to create map view: %d\n",GetLastError());

}


    for(index = 0;(message[index]=getchar()) != 0;index++);
    for(  i=0;i<strlen(message);i++){
    message[i]=message[i]-7;
                 }
    printf("Decrypter : %s\n",message);
start = pFile;
while(pFile < start + 50){

    *(pFile++) = 'A';
    break;

}
system("pause");
return 0;
           }

"..\def.h"

enter code here

          #ifndef __DEF_H
          #define __DEF_H
          #include <Windows.h>
           #include <stdio.h>
          //#include <stdlib.h>
          #define BUFF_SIZE 1024 *64
           #define FILE_NAME "log.txt"


          void exitPrompt(){
      system("pause");
     exit(0);
              }
                  #endif

Answer 1

你有很多问题:)

首先，在 Windows 下，内存映射文件无法扩展 - 这使得它们相当不适合写入日志文件。

同一个文件的多个 View 应该是连贯的，只要它们不引用网络位置并且你不混合内存映射和普通文件 I/O，所以应该可以编造一些东西这行得通……但是您需要一些方法来编排您的写入。

恐怕无法绕过某些进程间通信来安全地执行此操作。对于标准的 ASCII 日志文件，肯定没有，对于自定义二进制格式，您可能会使用长度前缀字符串和原子数据访问进行一些欺骗(尽管我不确定在写入内存映射文件时是否可以保证原子性)，但要正确地做到这一点将是一件棘手的事情——随着竞争条件的可能性而成熟。