Compress and then Decompress a string with zlib.

test.sh

# compile
$ g++ zlib-example.cpp -lz -o zlib-example

# run
$ ./zlib-example
Uncompressed size is: 36
Uncompressed string is: Hello Hello Hello Hello Hello Hello!

----------

Compressed size is: 13
Compressed string is: x��H���W��G*2

----------

Uncompressed size is: 36
Uncompressed string is: Hello Hello Hello Hello Hello Hello!

zlib-example.cpp

#include <stdio.h>
#include <string.h>  // for strlen
#include <assert.h>
#include "zlib.h"

// adapted from: http://stackoverflow.com/questions/7540259/deflate-and-inflate-zlib-h-in-c
int main(int argc, char* argv[])
{   
    // original string len = 36
    char a[50] = "Hello Hello Hello Hello Hello Hello!"; 

    // placeholder for the compressed (deflated) version of "a" 
    char b[50];

    // placeholder for the UNcompressed (inflated) version of "b"
    char c[50];
     

    printf("Uncompressed size is: %lu\n", strlen(a));
    printf("Uncompressed string is: %s\n", a);


    printf("\n----------\n\n");

    // STEP 1.
    // deflate a into b. (that is, compress a into b)
    
    // zlib struct
    z_stream defstream;
    defstream.zalloc = Z_NULL;
    defstream.zfree = Z_NULL;
    defstream.opaque = Z_NULL;
    // setup "a" as the input and "b" as the compressed output
    defstream.avail_in = (uInt)strlen(a)+1; // size of input, string + terminator
    defstream.next_in = (Bytef *)a; // input char array
    defstream.avail_out = (uInt)sizeof(b); // size of output
    defstream.next_out = (Bytef *)b; // output char array
    
    // the actual compression work.
    deflateInit(&defstream, Z_BEST_COMPRESSION);
    deflate(&defstream, Z_FINISH);
    deflateEnd(&defstream);
     
    // This is one way of getting the size of the output
    printf("Compressed size is: %lu\n", strlen(b));
    printf("Compressed string is: %s\n", b);
    

    printf("\n----------\n\n");


    // STEP 2.
    // inflate b into c
    // zlib struct
    z_stream infstream;
    infstream.zalloc = Z_NULL;
    infstream.zfree = Z_NULL;
    infstream.opaque = Z_NULL;
    // setup "b" as the input and "c" as the compressed output
    infstream.avail_in = (uInt)((char*)defstream.next_out - b); // size of input
    infstream.next_in = (Bytef *)b; // input char array
    infstream.avail_out = (uInt)sizeof(c); // size of output
    infstream.next_out = (Bytef *)c; // output char array
     
    // the actual DE-compression work.
    inflateInit(&infstream);
    inflate(&infstream, Z_NO_FLUSH);
    inflateEnd(&infstream);
     
    printf("Uncompressed size is: %lu\n", strlen(c));
    printf("Uncompressed string is: %s\n", c);
    

    // make sure uncompressed is exactly equal to original.
    assert(strcmp(a,c)==0);

    return 0;
}

Your length of array should be 51.

does this run on windows ?

when i am running this code this in giving me this error
error C2275: 'z_stream' : illegal use of this type as an expression

be ware using strlen() with binary data

// defstream.avail_in = (uInt)strlen(a)+1;

How to execute these programs in windows

does this run on windows ?

no ig

How to execute these programs in windows

install windows subsystem for linux and run the code from the linux environment

Input File: file size: 52946 Aug 23 17:23 RGB_16bits_palette_sample_image.png
Output Comp File: file size: 52972 Aug 23 17:35 zlib_comp_16bits.j2k
Output DeComp File: file size: 52946 Aug 23 17:35 zlib_decomp_16bits.png

Why the output Compressed file size becoming greater then the ( 52972 > 52946) Input file size ?

It's normal.
recompressing data almost always increases the size.

Is this possible without the array length? like instead of [90] we could have []?

Yes. without array length
use const char* myvar;

How do I use this dynamically without knowing the output size, (when decompressing)

@anasouardini Did you find any answer?