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fread and fwrite functions are the most efficient way to read or write large amounts of data.

Block I/O. fread and fwrite functions are the most efficient way to read or write large amounts of data. fread () – reads a specified number of bytes from a binary file and places them into memory at the specified location . prototype for fread ( ):

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fread and fwrite functions are the most efficient way to read or write large amounts of data.

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  1. Block I/O • fread and fwrite functions are the most efficient way to read or write large amounts of data. • fread() – reads a specified number of bytes from a binary file and places them into memory at the specified location. • prototype for fread( ): • intfread(void *InArea, intelementSize, int count, FILE *fp); • InArea – a pointer to the input area in memory. • elementSize– size of a basic data element, often specified using the sizeof operator • count – number of elements • fp – file pointer of an open file. • fread returns the number of items read.

  2. Block I/O • fwrite – writes the specified bytes of data from memory to the output file. • prototype for fwrite ( ): • intfwrite(void *OutArea, intelementSize, int count, FILE *fp); • OutArea – a pointer to memory holding the data to be written. • elementSize – size of a basic data element, often specified using the sizeofoperator • count – number of data elements • fp – file pointer of an open file. • fwrite copies elementSize * count bytes from the address specified by OutArea to the file. • fwrite returns the total number of characters written.

  3. Block input and output • Here is a more efficient implementation of the cat-like program that copies standard input to the standard output. • /* p12.c */ • #include <stdio.h> • main() • { • unsigned char *buff; • intlen = 0; • intiter = 0; • buff = malloc(1024); • if (buff == 0) • exit(1); • while ((len = fread(buff, 1, 1024, stdin)) != 0) • { • fwrite(buff, 1, len, stdout); • fprintf(stderr, "%d %d \n", iter, len); • iter += 1; • } • } • 0 322

  4. Block input and output Questions: Removing the parentheses surrounding (len = fread(buff, 1, 1024, stdin)) will break the program. Explain exactly how and whythings will go wrong in this case? What will happen if lenin the fwrite() is replaced by 1024?

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