c++ zlib库的使用

zlib是一个用于压缩和解压缩数据的开源库，它常于将文件或网络传输的数据进行压缩，以减少传输时间和网络流量。

下面是使用zlib库进行压缩和解压缩的示例代码：

压缩：

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <cstring>
#include "zlib.h"

bool compress(const std::string& in_file, const std::string& out_file)
{
    std::ifstream fin(in_file, std::ios::binary);
    if (!fin) {
        std::cerr << "Failed to open input file: " << in_file << std::endl;
        return false;
    }

    std::ofstream fout(out_file, std::ios::binary);
    if (!fout) {
        std::cerr << "Failed to open output file: " << out_file << std::endl;
        return false;
    }

    const int BUF_SIZE = 1024 * 8;
    char in_buf[BUF_SIZE];
    char out_buf[BUF_SIZE];

    z_stream zs;
    memset(&zs, 0, sizeof(zs));

    if (deflateInit(&zs, Z_DEFAULT_COMPRESSION) != Z_OK) {
        std::cerr << "Failed to initialize zlib compression" << std::endl;
        return false;
    }

    while (true) {
        fin.read(in_buf, BUF_SIZE);
        std::streamsize bytes_in = fin.gcount();
        if (bytes_in == 0) {
            break;
        }

        zs.next_in = reinterpret_cast<Bytef*>(in_buf);
        zs.avail_in = static_cast<uInt>(bytes_in);

        do {
            zs.next_out = reinterpret_cast<Bytef*>(out_buf);
            zs.avail_out = BUF_SIZE;

            int ret = deflate(&zs, Z_FINISH);
            if (ret == Z_STREAM_ERROR) {
                std::cerr << "Failed to compress input data" << std::endl;
                deflateEnd(&zs);
                return false;
            }

            std::streamsize bytes_out = BUF_SIZE - zs.avail_out;
            fout.write(out_buf, bytes_out);
        } while (zs.avail_out == 0);
    }

    deflateEnd(&zs);
    return true;
}

解压缩：

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <cstring>
#include "zlib.h"

bool decompress(const std::string& in_file, const std::string& out_file)
{
    std::ifstream fin(in_file, std::ios::binary);
    if (!fin) {
        std::cerr << "Failed to open input file: " << in_file << std::endl;
        return false;
    }

    std::ofstream fout(out_file, std::ios::binary);
    if (!fout) {
        std::cerr << "Failed to open output file: " << out_file << std::endl;
        return false;
    }

    const int BUF_SIZE = 1024 * 8;
    char in_buf[BUF_SIZE];
    char out_buf[BUF_SIZE];

    z_stream zs;
    memset(&zs, 0, sizeof(zs));

    if (inflateInit(&zs) != Z_OK) {
        std::cerr << "Failed to initialize zlib decompression" << std::endl;
        return false;
    }

    while (true) {
        fin.read(in_buf, BUF_SIZE);
        std::streamsize bytes_in = fin.gcount();
        if (bytes_in == 0) {
            break;
        }

        zs.next_in = reinterpret_cast<Bytef*>(in_buf);
        zs.avail_in = static_cast<uInt>(bytes_in);

        do {
            zs.next_out = reinterpret_cast<Bytef*>(out_buf);
            zs.avail_out = BUF_SIZE;

            int ret = inflate(&zs, Z_NO_FLUSH);
            if (ret == Z_STREAM_ERROR) {
                std::cerr << "Failed to decompress input data" << std::endl;
                inflateEnd(&zs);
                return false;
            }

            std::streamsize bytes_out = BUF_SIZE - zs.avail_out;
            fout.write(out_buf, bytes_out);
        } while (zs.avail_out == 0);
    }

    inflateEnd(&zs);
    return true;
}

在上述代码中，使用了z_stream结构体来保存压缩或解压缩的状态信息，其中deflateInit和inflateInit函数用于初始化z_stream结构体，deflate和inflate函数用于执行压缩和解压缩操作，deflateEnd和inflateEnd函数用于释放相关资源。

需要注意的是，压缩和解压缩的数据均应该是二进制数据，因此在打开文件时需要指定std::ios::binary标志。