LR函数研究fopen

首先，可以从LR函数帮助中查找到fopen函数定义如下，返回值是FILE *类型。FILE *fopen ( const char *filename, const char *access_mode );

我们再看看它给出的例子程序，发现将其返回值赋给长整形变量file_stream;

file_stream = fopen(filename, "r")== NULL ;

这里我不能理解，怎么不是赋给一个文件指针类型变量？望高手们回答……

Action() {

     int count, total = 0;
     char buffer[1000];
     long file_stream;
     char *filename = "c:\\readme.txt";

     /* Open the file with read access */
     if ((file_stream = fopen(filename, "r")) == NULL ) {

          lr_error_message("Cannot open %s", filename);
          return -1;
     }

     /* Read until end of file */
     while (!feof(file_stream)) {

          /* Read 1000 bytes while maintaining a running count */
          count = fread(buffer, sizeof(char), 1000, file_stream);
          lr_output_message("%3d read", count);

          /* Check for file I/O errors */
          if (ferror(file_stream)) {

               lr_output_message("Error reading file %s", filename);
               break;
          }

          total += count; /* add up actual bytes read */
     }

     /* Display final total */
     lr_output_message("Total number of bytes read = %d", total );

     /* Close the file stream */
     if (fclose(file_stream))
          lr_error_message("Error closing file %s", filename);

     return 0;
}