Problem to acess to a dynamic string

os2 · 03-25-2005, 09:20 AM

hi

in my main i do:

Code:

char *led_line=NULL;
searchFile(mnt_dir_led, "txt", led_line);

in my searchFile i do:

Code:

int searchFile(char *directory, char *ext, char *led_line)
{
  DIR *dirh;
  struct dirent *dirinfo;
  char *file_ext;
  int num = 0;
  
  dirh = opendir(directory);
  
  while(dirh)
  {
    if((dirinfo = readdir(dirh)) != NULL)
    {
      if((file_ext = strrchr(dirinfo->d_name, '.')) != NULL) 
        file_ext++;
      else 
        file_ext = dirinfo->d_name;
      
      if(!strcmp(file_ext, ext))
      {
        analyzeFilename(dirinfo->d_name, strlen(dirinfo->d_name), led_line);
      }
      num++;
    }
    else break;
  }
  closedir(dirh);  
  return num;
}

in my analyzeFileName i do:

Code:

void analyzeFilename(char *filename, int size, char *led_line)
{
    readFile(tmp_mnt_dir_led, size, mnt_dir_led, filename, led_line);
    printf("led_line: %s\n",led_line);

in my readFile i do:

Code:

void readFile(char *tmp_dir_led, int size, char *directory, char *filename, char *led_line)
{
    FILE *fp;
    char line[LINE_MAX];
    snprintf(tmp_mnt_dir_led, sizeof(tmp_mnt_dir_led),"%s/%s", directory,filename);        
    fp = fopen(tmp_mnt_dir_led, "r");
    if(fp!=NULL)
    {
        fgets(line, LINE_MAX, fp);
        if(led_line!=NULL)
             free(led_line);
        led_line=(char *) malloc (sizeof(line));
        strcpy(led_line,line);
    }
}

why in my analyzeFilename function, after the call function to readFile i get NULL when i printf led_line?

i want to do some action to led_line after the readFile... but i get NULL

how to resolve that?

thanks

TheLinuxDuck · 03-25-2005, 10:19 AM

The first and best thing you can do is error check the malloc call:

Code:

void someFunction(void)
{
  char * ptr;

  ptr = (char *)malloc(sizeof(char) * 100);
  if(ptr == NULL) {
    perror("Malloc on ptr failed");
    return;
  }

  //  something fancy done here

  free(ptr);
}

The other thing I noticed is that, if the file open fails, the code does not produce any kind of error message. That would be another good idea.