c++ Zlib fwrite to file not working - c++

Question

I have this procedure I'm working on, to simply do the following:
Open a gzipped file
Uncompress it to a std::string
Compress it from a std::string
Save as gzipped file
However, I cannot seem to write the gzipped data at the end. The error I'm getting is :No Matching Function Call to 'fwrite'.
Am I feeding it the wrong parameters? Or an incorrect type?
Here's the full procedure:
#include <iostream>
#include "zlib-1.2.8/zlib.h"
#include <stdexcept>
#include <iomanip>
#include <sstream>
#include <stdio.h>
#include <assert.h>
#include <cstdio>
#include <string>
#include <cstring>
#include <cstdlib>
#include "zlib.h"
#include "zconf.h"
#if defined(MSDOS) || defined(OS2) || defined(WIN32) || defined(__CYGWIN__)
# include <fcntl.h>
# include <io.h>
# define SET_BINARY_MODE(file) setmode(fileno(file), O_BINARY)
#else
# define SET_BINARY_MODE(file)
#endif
#define CHUNK 16384
using namespace std;
bool gzipInflate( const std::string& compressedBytes, std::string& uncompressedBytes ) {
if ( compressedBytes.size() == 0 ) {
uncompressedBytes = compressedBytes ;
return true ;
}
uncompressedBytes.clear() ;
unsigned full_length = compressedBytes.size() ;
unsigned half_length = compressedBytes.size() / 2;
unsigned uncompLength = full_length ;
char* uncomp = (char*) calloc( sizeof(char), uncompLength );
z_stream strm;
strm.next_in = (Bytef *) compressedBytes.c_str();
strm.avail_in = compressedBytes.size() ;
strm.total_out = 0;
strm.zalloc = Z_NULL;
strm.zfree = Z_NULL;
bool done = false ;
if (inflateInit2(&strm, (16+MAX_WBITS)) != Z_OK) {
free( uncomp );
return false;
}
while (!done) {
// If our output buffer is too small
if (strm.total_out >= uncompLength ) {
// Increase size of output buffer
char* uncomp2 = (char*) calloc( sizeof(char), uncompLength + half_length );
memcpy( uncomp2, uncomp, uncompLength );
uncompLength += half_length ;
free( uncomp );
uncomp = uncomp2 ;
}
strm.next_out = (Bytef *) (uncomp + strm.total_out);
strm.avail_out = uncompLength - strm.total_out;
// Inflate another chunk.
int err = inflate (&strm, Z_SYNC_FLUSH);
if (err == Z_STREAM_END) done = true;
else if (err != Z_OK) {
break;
}
}
if (inflateEnd (&strm) != Z_OK) {
free( uncomp );
return false;
}
for ( size_t i=0; i<strm.total_out; ++i ) {
uncompressedBytes += uncomp[ i ];
}
free( uncomp );
return true ;
}
/** Compress a STL string using zlib with given compression level and return
* the binary data. */
std::string compress_string(const std::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
std::ostringstream oss;
oss << "Exception during zlib compression: (" << ret << ") " << zs.msg;
throw(std::runtime_error(oss.str()));
}
return outstring;
}
/* Reads a file into memory. */
bool loadBinaryFile( const std::string& filename, std::string& contents ) {
// Open the gzip file in binary mode
FILE* f = fopen( filename.c_str(), "rb" );
if ( f == NULL )
return false ;
// Clear existing bytes in output vector
contents.clear();
// Read all the bytes in the file
int c = fgetc( f );
while ( c != EOF ) {
contents += (char) c ;
c = fgetc( f );
}
fclose (f);
return true ;
}
int main(int argc, char *argv[]) {
// Read the gzip file data into memory
std::string fileData ;
if ( !loadBinaryFile( "myfilein.gz", fileData ) ) {
printf( "Error loading input file." );
return 0 ;
}
// Uncompress the file data
std::string data ;
if ( !gzipInflate( fileData, data ) ) {
printf( "Error decompressing file." );
return 0 ;
}
// Print the data
printf( "Data: \"" );
for ( size_t i=0; i<data.size(); ++i ) {
printf( "%c", data[i] );
}
printf ( "\"\n" );
std::string outy;
// Compress the file data
outy = compress_string(data, 0);
//Write the gzipped data to a file.
FILE *handleWrite=fopen("myfileout.gz","wb");
fwrite(outy,sizeof(outy),1,handleWrite);
fclose(handleWrite);
return 0;
}

Answer 1

std::string cannot be cast to void* (what fwrite expects).
Try:
fwrite(outy.data(),outy.size(),1,handleWrite);
Although I'm not sure if storing binary data inside std::string is a good idea.