Convert 4-bit P5 format PGM file to C array

pgm2array.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int convert(const char *var, FILE *in, FILE *out) {
  char buf[256];
  char fmt[16] = { 0 };
  int width = 0, height = 0, depth = 0;

  fgets(buf, sizeof(buf), in); // format
  sscanf(buf, "%s", fmt);

  fgets(buf, sizeof(buf), in); // image size
  sscanf(buf, "%d %d", &width, &height);

  fgets(buf, sizeof(buf), in); // bit depth
  sscanf(buf, "%d", &depth);

  // fprintf(stdout, "%s\n%d %d\n%d\n", fmt, width, height, depth);

  if ((width & 1) != 0) {
    fprintf(stderr, "error: even width is required: %d\n", width);
    return -1;
  }

  if (depth != 15) { // 4-bit max value
    fprintf(stderr, "error: only 4-bit depth is supported: %d\n", depth);
    return -1;
  }

  fprintf(out, "unsigned char %s[] = {\n", var);
  int i = 0, hi = 0;
  for (i = 1; i <= width * height; i++) {
    hi = fgetc(in);
    if (hi == EOF) {
      fprintf(stderr, "error: unexpected EOF\n");
      return -1;
    }

    fprintf(out, "0x%x, ", hi);
    if (i % width == 0) {
      fprintf(out, "\n");
    }
  }
  fprintf(out, "};\n");

  return 0;
}

int main(int argc, char *argv[]) {
  int i;
  for (i = 1; i < argc; i++) {

    FILE *fin = fopen(argv[i], "r");

    // remove file extension
    *strrchr(argv[i], '.') = '\0';

    // construct filename
    char fname[256] = { 0 };
    snprintf(fname, sizeof(fname), "%s.c", argv[i]);

    FILE *fout = fopen(fname, "w");

    if (fin != NULL && fout != NULL) {
      if (convert(argv[i], fin, fout) < 0) {
        fprintf(stderr, "error: failed to convert %s\n", argv[i]);
      }

      fclose(fin);
      fclose(fout);
    }
  }

  exit(EXIT_SUCCESS);
}