compress_string.h

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#ifndef _COMPRESS_STRING_H
#define _COMPRESS_STRING_H
 
#include <string>
#include <zlib.h>
using namespace std;
 
string compress_string(const string& str, int compressionlevel = Z_BEST_COMPRESSION)
{
    z_stream zs;                        // z_stream is zlib's control structure
    memset(&zs, 0, sizeof(zs));
    
    if (deflateInit(&zs, compressionlevel) != Z_OK)
        throw(std::runtime_error("deflateInit failed while compressing."));
    
    zs.next_in = (Bytef*)str.data();
    zs.avail_in = str.size();           // set the z_stream's input
    
    int ret;
    char outbuffer[32768];
    std::string outstring;
    
    // retrieve the compressed bytes blockwise
    do {
        zs.next_out = reinterpret_cast<Bytef*>(outbuffer);
        zs.avail_out = sizeof(outbuffer);
        
        ret = deflate(&zs, Z_FINISH);
        
        if (outstring.size() < zs.total_out) {
            // append the block to the output string
            outstring.append(outbuffer,
                             zs.total_out - outstring.size());
        }
    } while (ret == Z_OK);
    
    deflateEnd(&zs);
    
    if (ret != Z_STREAM_END) {          // an error occurred that was not EOF
        ostringstream oss;
        oss << "Exception during zlib compression: (" << ret << ") " << zs.msg;
        throw(runtime_error(oss.str()));
    }
    
    return outstring;
}
 
 
string decompress_string(const string& str)
{
    z_stream zs;                        // z_stream is zlib's control structure
    memset(&zs, 0, sizeof(zs));
    
    if (inflateInit(&zs) != Z_OK)
        throw(std::runtime_error("inflateInit failed while decompressing."));
    
    zs.next_in = (Bytef*)str.data();
    zs.avail_in = str.size();
    
    int ret;
    char outbuffer[32768];
    std::string outstring;
    
    // get the decompressed bytes blockwise using repeated calls to inflate
    do {
        zs.next_out = reinterpret_cast<Bytef*>(outbuffer);
        zs.avail_out = sizeof(outbuffer);
        
        ret = inflate(&zs, 0);
        
        if (outstring.size() < zs.total_out) {
            outstring.append(outbuffer,
                             zs.total_out - outstring.size());
        }
        
    } while (ret == Z_OK);
    
    inflateEnd(&zs);
    
    if (ret != Z_STREAM_END) {          // an error occurred that was not EOF
        std::ostringstream oss;
        oss << "Exception during zlib decompression: (" << ret << ") "
        << zs.msg;
        throw(std::runtime_error(oss.str()));
    }
    
    return outstring;
}
 
#endif