进程间通过内核对象共享数据失败：OpenFileMapping返回NULL

我正在学习Pavel Yosifovich的书籍和视频，尝试用纯C编写程序，通过内核对象实现两个进程间的文本字符串传递。但读取进程中OpenFileMapping始终返回NULL，GetLastError返回错误码2（文件未找到）。我用WinObj工具看到MySharedMemory对象存在于\Sessions\2\BaseNamedObjects\MySharedMemory路径下，排除了权限问题，尝试将名称改为Local\MySharedMemory也没用，管理员身份运行同样无法解决，推测是路径相关问题。

初始代码 #

生产者代码 #

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

int main() {
    HANDLE hFileMapping;
    LPVOID lpFileMap;
    char buffer[] = "Windows System Programming is fun!";

    hFileMapping = CreateFileMapping(
        INVALID_HANDLE_VALUE,
        NULL,
        PAGE_READWRITE,
        0,
        sizeof(buffer),
        L"MySharedMemory"
        );

    if (hFileMapping == NULL) {
        printf("Error creating file mapping: %d\n", GetLastError());
        return 1;
    }

    lpFileMap = MapViewOfFile(hFileMapping, FILE_MAP_WRITE, 0, 0, 0);

    if (lpFileMap == NULL) {
        printf("Error mapping view of file: %d\n", GetLastError());
        CloseHandle(hFileMapping);
        return 1;
    }

    strcpy((char*)lpFileMap, buffer);
    printf("Data written to shared memory.  Press Enter to exit...\n");
    getchar();
    UnmapViewOfFile(lpFileMap);
    CloseHandle(hFileMapping);
    return 0;
}

消费者代码 #

#include <windows.h>
#include <stdio.h>

int main() {
    HANDLE hFileMapping;
    LPVOID lpFileMap;

    hFileMapping = OpenFileMapping(
        FILE_MAP_READ,
        FALSE,
        L"MySharedMemory"
        );

    if (hFileMapping == NULL) {
        printf("Error opening file mapping: %d\n", GetLastError());
        getchar();
        return 1;
        
    }

    lpFileMap = MapViewOfFile(
        hFileMapping,
        FILE_MAP_READ,
        0,
        0,
        0,
        0
        );

    if (lpFileMap == NULL) {
        printf("Error mapping view of file: %d\n", GetLastError());
        CloseHandle(hFileMapping);
        getchar();
        return 1;
    }

    printf("Received message: %s\n", (char*)lpFileMap);
    UnmapViewOfFile(lpFileMap);
    getchar();
    CloseHandle(hFileMapping);
    return 0;
}

修改后的代码（仍无法运行） #

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

int main() {
    HANDLE hFileMapping;
    LPVOID lpFileMap;
    char buffer[] = "Windows System Programming is fun!";

    hFileMapping = CreateFileMapping(
        INVALID_HANDLE_VALUE,
        NULL,
        PAGE_READWRITE,
        0,
        1 << 12,
        L"MySharedMemory"
        );

    if (hFileMapping == NULL) {
        printf("Error creating file mapping: %d\n", GetLastError());
        return 1;
    }

    lpFileMap = MapViewOfFile(hFileMapping, FILE_MAP_WRITE, 0, 0, 0);

    if (lpFileMap == NULL) {
        printf("Error mapping view of file: %d\n", GetLastError());
        CloseHandle(hFileMapping);
        return 1;
    }

    strcpy((char*)lpFileMap, buffer);
    printf("Data written to shared memory.  Press Enter to exit...\n");
    getchar();
    UnmapViewOfFile(lpFileMap);
    CloseHandle(hFileMapping);
    return 0;
}



#include <windows.h>
#include <stdio.h>

int main() {
    HANDLE hFileMapping;
    LPVOID lpFileMap;

    //hFileMapping = OpenFileMapping(
    //  FILE_MAP_READ,
    //  FALSE,
    //  L"MySharedMemory"
    //  );

    hFileMapping = CreateFileMapping(
        INVALID_HANDLE_VALUE,
        NULL,
        PAGE_READWRITE,
        0,
        1 << 12,
        L"MySharedMemory"
        );

    if (hFileMapping == NULL) {
        printf("Error opening file mapping: %d\n", GetLastError());
        getchar();
        return 1;
        
    }

    lpFileMap = MapViewOfFile(
        hFileMapping,
        FILE_MAP_READ,
        0,
        0,
        1 << 12
        );

    if (lpFileMap == NULL) {
        printf("Error mapping view of file: %d\n", GetLastError());
        CloseHandle(hFileMapping);
        getchar();
        return 1;
    }

    printf("Received message: %s\n", (char*)lpFileMap);
    UnmapViewOfFile(lpFileMap);
    getchar();
    CloseHandle(hFileMapping);
    return 0;
}

问题排查与解决 #

1. 字符集不匹配：检查两个项目的编译字符集设置，必须保持一致（要么均为Unicode，要么均为多字节字符集）。如果生产者用Unicode编译（带L前缀），消费者用多字节编译，会导致名称解析不匹配。统一字符集后，确保共享内存名称的写法完全一致（Unicode用L"xxx"，多字节用"xxx"）。

2. 会话与命名空间问题：如果两个进程不在同一个会话，尝试在名称前添加Global\前缀（需管理员权限），比如L"Global\\MySharedMemory"，且生产者和消费者必须使用相同前缀。

3. 生产者提前销毁对象：生产者在getchar()后立即关闭句柄并销毁映射，若此时消费者未运行，共享内存对象会被系统回收。确保消费者运行时，生产者仍保持句柄打开。

4. 消费者代码逻辑错误：修改后的消费者用CreateFileMapping替代OpenFileMapping，会创建新的共享内存对象而非打开已有对象。应恢复使用OpenFileMapping，并保证名称与生产者完全一致。

修正后的消费者示例（Unicode字符集）：

#include <windows.h>
#include <stdio.h>

int main() {
    HANDLE hFileMapping;
    LPVOID lpFileMap;

    hFileMapping = OpenFileMapping(
        FILE_MAP_READ,
        FALSE,
        L"MySharedMemory"
        );

    if (hFileMapping == NULL) {
        printf("Error opening file mapping: %d\n", GetLastError());
        getchar();
        return 1;
        
    }

    lpFileMap = MapViewOfFile(
        hFileMapping,
        FILE_MAP_READ,
        0,
        0,
        0
        );

    if (lpFileMap == NULL) {
        printf("Error mapping view of file: %d\n", GetLastError());
        CloseHandle(hFileMapping);
        getchar();
        return 1;
    }

    printf("Received message: %s\n", (char*)lpFileMap);
    UnmapViewOfFile(lpFileMap);
    getchar();
    CloseHandle(hFileMapping);
    return 0;
}

内容的提问来源于stack exchange，提问作者Chad Botting