Advantage of Pointer | C Language

Advantage of Pointer

• It provides dynamic programming environment.
• Physical location of memory can be direct access through pointer.
• It allow to call by reference to function which help to achieved many dynamic operation.
• Dynamic memory allocation is achieved through array.
• Fire read write operations are achieved through pointer.
• Management of structures which are allocated memory dynamically is efficiently achieved by pointer.

File read write function | C Language

1. ftell()

Returns the current file pointer position in numeric form. 

 Declaration:  long ftell(FILE *stream);

 

 Remarks:

ftell returns the current file pointer for stream.If the file is binary, the offset is measured in bytes from the beginning of

the file The value returned by ftell can be used in a subsequent call to fseek.

 

 Return Value:

   On success, returns the current file pointer position.

   On error, returns -1L and sets errno to a positive value.

 

Example

 

    #include <stdio.h>

 

int main(void)

{

   FILE *stream;

 

   stream = fopen("MYFILE.TXT", "w+");

   fprintf(stream, "This is a test");

   printf("The file pointer is at byte %ld\n", ftell(stream));

   fclose(stream);

   return 0;

}

2. rewind()

Repositions file pointer to stream's beginning

 

 Syntax:

  void rewind(FILE *stream);

 

 Remarks:

rewind(stream) is equivalent to   fseek(stream, 0L, SEEK_SET) 

except that rewind clears the end-of-file and error indicators, while fseek

only clears the end-of-file indicator. 

After rewind, the next operation on an update file can be either input or

output.

 

Example

 

 #include <stdio.h>

 #include <dir.h>

 

 int main(void)

 {

    FILE *fp;

    char *fname = "TXXXXXX", *newname, first;

 

    newname = mktemp(fname);

    fp = fopen(newname,"w+");

    fprintf(fp,"abcdefghijklmnopqrstuvwxyz");

    rewind(fp);

    fscanf(fp,"%c",&first);

    printf("The first character is: %c\n",first);

    fclose(fp);

    remove(newname);

 

    return 0;

}

 

Next Topic

Memory Allocation Function

 

1. Malloc

Full form of malloc function is memory allocate. malloc allocates a block of size bytes from the memory heap. It allows a program to allocate memory explicitly as it's needed, and in the exact amounts needed.

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