C++文件格式验证 魔法数字检测方法

#include 
#include 
#include 
#include 

std::vector readMagicNumber(const std::string& filepath, size_t length) {
    std::ifstream file(filepath, std::ios::binary);
    if (!file) {
        throw std::runtime_error("无法打开文件");
    }

    std::vector magic(length);
    file.read(reinterpret_cast(magic.data()), length);

    if (file.gcount() < static_cast(length)) {
        throw std::runtime_error("文件太短，无法读取足够的字节");
    }

    return magic;
}

bool matches(const std::vector& data, const std::vector& signature) {
    if (data.size() < signature.size()) return false;
    for (size_t i = 0; i < signature.size(); ++i) {
        if (data[i] != signature[i]) return false;
    }
    return true;
}

std::string detectFileType(const std::string& filepath) {
    auto magic = readMagicNumber(filepath, 8); // 读取前8字节

    // 检测PNG
    if (matches(magic, {0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A})) {
        return "PNG";
    }
    // 检测JPEG
    if (matches(magic, {0xFF, 0xD8, 0xFF})) {
        return "JPEG";
    }
    // 检测GIF
    if (matches(magic, {0x47, 0x49, 0x46, 0x38})) {
        return "GIF";
    }
    // 检测BMP
    if (matches(magic, {0x42, 0x4D})) {
        return "BMP";
    }
    // 检测PDF
    if (matches(magic, {0x25, 0x50, 0x44, 0x46})) {
        return "PDF";
    }

    return "未知格式";
}

int main() {
    try {
        std::string type = detectFileType("test.png");
        std::cout << "文件类型: " << type << std::endl;
    } catch (const std::exception& e) {
        std::cerr << "错误: " << e.what() << std::endl;
    }
    return 0;
}