How to use the dwg_add_TEXT function correctly

[fly-sure]

I tried to write text to a dwg file using dwg_add_TEXT but it didn't work and after running the executable the dwg file became unopenable. When opening a file, it prompts that the loading failed.Could you help me figure out what the problem is?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dwg.h>
#include <time.h>
#include <unistd.h>
#include "dwg_api.h"

static int add_text(Dwg_Data *dwg, dwg_point_3d *pt)
{
  int error = 0;
  char text[128];
  double height = dwg->header_vars.TEXTSIZE;
  time_t t = time (NULL);
  Dwg_Object_BLOCK_HEADER *hdr = dwg_get_block_header (dwg, &error);
  Dwg_Entity_TEXT *ent;

    if (error || !hdr) {
        fprintf(stderr, "Error retrieving block header: %d\n", error);
        return 1;
    }

    if (height <= 0) {
        height = 2.5; 
    }

  strftime (text, sizeof (text), "Last updated: %c", localtime (&t));

  if ((ent = dwg_add_TEXT (hdr, text, pt, height)))
    {
      ent->horiz_alignment = HORIZ_ALIGNMENT_RIGHT;
      return 0;
    }

    return 1;
}

int main() {
    int result=0;
    const char *filename = "test.dwg"; 
    Dwg_Data dwg;
    dwg_point_3d pt;

    memset (&dwg, 0, sizeof (Dwg_Data));

    result = dwg_read_file(filename, &dwg); 
    printf("%d\n", result);
    if (result != 0) {  
        fprintf(stderr, "Failed to open DWG file: %s\n", filename);
        return 1; 
    }else {
         printf("Successfully opened DWG file: %s\n", filename);
    }

    // get the insertion point for text
    //pt.x = dwg.header_vars.LIMMAX.x;
    //pt.y = dwg.header_vars.LIMMAX.y;
    pt.x = 100;
    pt.y = 100;
    pt.z = 0.0;

    if (add_text(&dwg, &pt) == 0) {
        fprintf(stderr, "Text added at (%f, %f)\n", pt.x, pt.y);
    } else {
        fprintf(stderr, "Failed to add text.\n");
    }

    unlink (filename);
  if (dwg.header.version > R_2000)
    dwg.header.version = R_2000;

    result = dwg_write_file (filename, &dwg);
    printf("%d\n", result);
    if (result != 0) {
     fprintf(stderr, "Failed to write DWG file: %s\n", filename);
    } else {
        printf("Successfully updated DWG file: %s\n", filename);
    }

    dwg_free(&dwg); 
    printf("Successfully closed DWG file: %s\n", filename);

    return 0; 
}