How to use stb_image_write?

I had a hard time trying to use stb_image_write.h since the documentation of it is not complete. There is little description about how to use it correctly.

And I got one example of using it. So, I added my code here for others who is struggling to use it, also adding the result image.

#include <iostream>
#include <fstream>
#include <sstream>

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

#define STBI_MSC_SECURE_CRT
#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"

int main()
{
 const int width = 200;
 const int height = 100;
#define CHANNEL_NUM 3

 /*** NOTICE!! You have to use uint8_t array to pass in stb function  ***/
 // Because the size of color is normally 255, 8bit.
 // If you don't use this one, you will get a weird imge.
 uint8_t* pixels = new uint8_t[width * height * CHANNEL_NUM];

 int index = 0;
 for (int j = height - 1; j >= 0; --j)
 {
  for (int i = 0; i < width; ++i)
  {
   float r = (float)i / (float)width;
   float g = (float)j / (float)height;
   float b = 0.2f;
   int ir = int(255.99 * r);
   int ig = int(255.99 * g);
   int ib = int(255.99 * b);

   pixels[index++] = ir;
   pixels[index++] = ig;
   pixels[index++] = ib;
  }
 }
 
 // if CHANNEL_NUM is 4, you can use alpha channel in png
 stbi_write_png("stbpng.png", width, height, CHANNEL_NUM, pixels, width * CHANNEL_NUM);

 // You have to use 3 comp for complete jpg file. If not, the image will be grayscale or nothing.
 stbi_write_jpg("stbjpg3.jpg", width, height, 3, pixels, 100);
 delete[] pixels;

 return 0;
}

"#define STBI_MSC_SECURE_CRT" enables the Visual Studio to compile the source.
If you don't use the Visual Studio, you need not use it.

And Finally, Both of the result images are same.

png result:

jpg result: