如何使用C/C++在公共目录创建文件?

Question

需要在native侧实现输出文件到公共目录，有没有什么方法能够实现使用C/C++的方法直接在公共目录创建文件呢？

Answer 1

通常涉及到几个关键步骤，包括确定目标平台的文件系统路径、获取适当的文件访问权限，以及使用C/C++标准库函数（如fopen, fwrite等）或平台特定的API来创建和操作文件。

Answer 2

在原生native侧使用C/C++在公共目录Android，iOS，Win，创建文件是常见的需求，特别是当开发跨平台应用使用JNI在Android上，或使用Objective-C/Swift在iOS上时。

1. 使用标准库函数

   #include <fstream>
   #include <iostream>
   
   int main() {
    // 指定公共目录的路径
    const char* publicDirPath = "/path/to/public/directory/";
    const char* filename = "output_file.txt";
    
    // 创建完整的文件路径
    std::string fullPath = std::string(publicDirPath) + filename;
   
    // 使用 std::ofstream 创建文件
    std::ofstream outFile(fullPath);
    if (outFile.is_open()) {
        outFile << "Hello, World!" << std::endl;
        outFile.close();
        std::cout << "File created successfully at " << fullPath << std::endl;
    } else {
        std::cerr << "Error creating file at " << fullPath << std::endl;
    }
   
    return 0;
   }
   

2. 使用系统调用如 Linux 或 macOS

   #include <unistd.h>
   #include <fcntl.h>
   #include <sys/stat.h>
   #include <iostream>
   
   int main() {
    // 指定公共目录的路径
    const char* publicDirPath = "/path/to/public/directory/";
    const char* filename = "output_file.txt";
   
    // 创建完整的文件路径
    std::string fullPath = std::string(publicDirPath) + filename;
   
    // 使用 open() 创建文件
    int fd = open(fullPath.c_str(), O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
    if (fd == -1) {
        std::cerr << "Error creating file at " << fullPath << std::endl;
        return 1;
    }
   
    const char* data = "Hello, World!";
    ssize_t bytesWritten = write(fd, data, strlen(data));
    if (bytesWritten == -1) {
        std::cerr << "Error writing to file" << std::endl;
        close(fd);
        return 1;
    }
   
    close(fd);
    std::cout << "File created successfully at " << fullPath << std::endl;
   
    return 0;
   }
   

3. Windows 系统调用

   #include <windows.h>
   #include <iostream>
   
   int main() {
    // 指定公共目录的路径
    const char* publicDirPath = "C:\\path\\to\\public\\directory\\";
    const char* filename = "output_file.txt";
   
    // 创建完整的文件路径
    std::string fullPath = std::string(publicDirPath) + filename;
   
    // 使用 CreateFile() 创建文件
    HANDLE hFile = CreateFile(fullPath.c_str(), GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
    if (hFile == INVALID_HANDLE_VALUE) {
        std::cerr << "Error creating file at " << fullPath << std::endl;
        return 1;
    }
   
    const char* data = "Hello, World!";
    DWORD bytesWritten;
    BOOL writeResult = WriteFile(hFile, data, strlen(data), &bytesWritten, NULL);
    if (!writeResult) {
        std::cerr << "Error writing to file" << std::endl;
        CloseHandle(hFile);
        return 1;
    }
   
    CloseHandle(hFile);
    std::cout << "File created successfully at " << fullPath << std::endl;
   
    return 0;
   }