c++ - 如果保存数据，libz 压缩失败

Question

我刚刚遇到了 libz 的一个非常奇怪的行为。如果我只是使用 compress 功能一切正常，但如果我尝试，例如。将压缩数据保存到文件，我收到 Z_BUF_ERROR。我做错了什么？

#include <iostream>
#include <fstream>

#include "zlib.h"

typedef unsigned char byte_t;

static int read_filesize(const char* filename) {
    int size = -1;
    std::ifstream file(filename);
    if (!file.is_open()) return size;

    file.seekg(0, std::ios::end);
    size = (int) file.tellg();
    file.close();

    return size;
}

static bool read_binary_file(const char* filename, byte_t* dst, const unsigned length) {
    std::ifstream file(filename, std::ios::binary);
    if (!file.is_open()) return false;

    file.read((char*) dst, length);
    file.close();

    return true;
}

static bool save_binary_file(const char* filename, const byte_t* src, const unsigned length) {
    std::ofstream file(filename, std::ios::binary);
    if (!file.is_open()) return false;

    file.write((const char*) src, length);
    file.close();

    return true;
}

int main(int args, char **argv) {
    int fileSize = read_filesize(argv[1]);
    byte_t fileData[fileSize];
    bool result = read_binary_file(argv[1], fileData, fileSize);

    unsigned compressedSize = compressBound(fileSize);
    byte_t compressed[compressedSize]; 

    int compressionResult = compress(compressed, (unsigned long*) &compressedSize, fileData, fileSize);

    switch (compressionResult) {
    case Z_OK:
        std::cout << "Compression succeeded!\n";
        break;

    case Z_MEM_ERROR:
        std::cout << "Error: Z_MEM_ERROR!\n";
        return 1;

    case Z_BUF_ERROR:
        std::cout << "Error: Z_BUF_ERROR!\n";
        return 1;

    default:
        std::cout << "Error: UNDEFINED!\n";
        return 1;
    }

    std::cout << "Size of '" << argv[1] << "': " << fileSize << "\n"
            << "After: " << compressedSize << "\n";

    bool saveResult = save_binary_file("file.bin.z", compressed, compressedSize);  // everything works if I remove this instruction

    return 0;
}

Answer 1

从上面的评论看来，您使用的是 64 位架构，其中 sizeof(unsigned long)==8，而 sizeof(unsigned)==4。

因此，转换 (unsigned long*)&compressedSize 其中 compressedSize 是 unsigned 类型，产生未定义的行为。

只需将 compressedSize 的声明更改为类型 unsigned long 即可解决此问题。