Write an image row by row with libpng using C - c

Question

I'm trying to create a png image with the libpng library using C (gcc on linux).
This should expose my problem:
void createPng(char *filename, int width, int height) {
FILE *fp = fopen(filename, "wb");;
png_bytep row = NULL;
png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
png_infop info_ptr = png_create_info_struct(png_ptr);
setjmp(png_jmpbuf(png_ptr));
png_init_io(png_ptr, fp);
png_set_IHDR(png_ptr, info_ptr, width, height,
8, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
png_text title_text;
title_text.compression = PNG_TEXT_COMPRESSION_NONE;
title_text.key = "Title";
title_text.text = "My title";
png_set_text(png_ptr, info_ptr, &title_text, 1);
png_write_info(png_ptr, info_ptr);
row = (png_bytep) malloc(sizeof(png_byte)*width*3); //I think the problems start here
for(int y=0; y<height; y++) {
for(int x=0; x<width; x++) {
row[x*3] = 0; //Red
row[x*3+1] = 0; //Green
row[x*3+2] = 0; //Blue
}
png_write_row(png_ptr, row); //I think this causes the segmentation fault
}
png_write_end(png_ptr, row);
}
In my mind this function should create a black image, the problem is that the execution stops with a segmentation fault. I think this happens because I'm not passing a well created png_bytep to png_write_row.
I know it isn't a good pratice to not check if all these function calls (in the first part of the program) return a valid pointer (and not NULL). Nevertheless I chose to post a minimal code without the checks but I've verified that the problem isn't there.

Answer 1

The code is OK, except for that last line:
png_write_end(png_ptr, row);
This should be ...
png_write_end(png_ptr, info_ptr);
because the png_write_end() function takes an info_ptr (whatever that is) as the second argument.
Other than that, the code works fine.
Thanks for a good starting-point-example of writing a PNG image line-by-line.