I can't resize image with stb_image_resize.h

Question

I make image to ASCII converter and I try to resize image using stb_image_resize.h for better result, but i get segmentation fault when resizing the image or in some cases asserts -- STBIR_ASSERT (info->channels >= 0) or STBIR_ASSERT (info->channels <= MAX_CHANNELS). I tried to do like in this answer https://stackoverflow.com/a/65873156, but it doesn't work.

prefixes

#include <iostream>
#include <fstream>
#include <cassert>
#include <cstring>
#include <stdint.h>


#define STB_IMAGE_IMPLEMENTATION
#define STB_IMAGE_WRITE_IMPLEMENTATION
#define STB_IMAGE_RESIZE_IMPLEMENTATION



unsigned char* stbir_malloc(size_t size, void* context){
    return (unsigned char *) malloc(size);
}

void stbir_free(void* memory, void* context){
    memory = nullptr;
    context = nullptr;
}


#define STBIR_MALLOC stbir_malloc
#define STBIR_FREE stbir_free


#include "stb_image.h"
#include "stb_image_write.h"
#include "stb_image_resize.h"

Image structure(took from https://youtu.be/028GNYC32Rg)

struct Image {
  uint8_t* data = NULL;
  size_t size = 0;
  int w;
  int h;
  int channels;

  Image(const char* filename){
    if (read(filename)){
      printf("Read %s\n", filename);
      size = w*h*channels;
    } else {
      printf("Failed to read %s\n", filename);
    }
  }
  Image(int w, int h, int channels) : w(w), h(h), channels(channels){
    size = w*h*channels;
    data =  new uint8_t[size];
  }
  Image(const Image& image) : Image(image.w, image.h, image.channels){
    memcpy(data, image.data, size);
  }

  ~Image(){
    stbi_image_free(data);
  }

Resize function

 Image& resize(int width, int height){
        unsigned char* resizedPixels = nullptr;
        stbir_resize_uint8(data, w, h, 0, resizedPixels, width, height, 0, channels);
        stbi_image_free(data);
        data = resizedPixels;
        w = width;
        h = height;
        size = w*h*channels;
         return *this;
 }

Edit: I've used GDB and don't understand how alloc_context is equal to 0x0:

165        
(gdb) n

Breakpoint 1, stbir_malloc (size=65280, context=0x0) at ascii.cpp:15
15      //1 breakpoint
(gdb) n
16      return (unsigned char *) malloc(size);
(gdb) n
stbir__resize_arbitrary (alloc_context=0x0, input_data=0x7ffff78f7010, input_w=600, input_h=300, input_stride_in_bytes=0, output_data=0x0, output_w=300, output_h=150, output_stride_in_bytes=0, s0=0, t0=0, s1=1, t1=1, transform=0x0, channels=3, alpha_channel=-1, flags=0, type=STBIR_TYPE_UINT8, h_filter=STBIR_FILTER_DEFAULT, v_filter=STBIR_FILTER_DEFAULT, edge_horizontal=STBIR_EDGE_CLAMP, edge_vertical=STBIR_EDGE_CLAMP, colorspace=STBIR_COLORSPACE_LINEAR) at /media/D/workspaceOfC++/projects/quickStuff/ASCII/stb_image_resize.h:2448
2448       if (!extra_memory)
(gdb) n
2451       result = stbir__resize_allocated(&info, input_data, input_stride_in_bytes,
(gdb) n

Program received signal SIGSEGV, Segmentation fault.
0x000055555557b01a in stbir__encode_scanline (stbir_info=0x7fffffffe070, num_pixels=300, output_buffer=0x0, encode_buffer=0x5555555a6f40, channels=3, alpha_channel=-1, decode=0) at /media/D/workspaceOfC++/projects/quickStuff/ASCII/stb_image_resize.h:1755
1755                       ((unsigned char*)output_buffer)[index] = STBIR__ENCODE_LINEAR8(encode_buffer[index]);
(gdb) n

Program terminated with signal SIGSEGV, Segmentation fault.
The program no longer exists.
(gdb) 
The program is not being run.
(gdb) 
The program is not being run.
(gdb) q

I've solved the problem, it was because resizedPixels was equal to nullptr, after i've changed it to (unsigned char *) malloc(width * height * 3), it converted image. Thanks for help :)