fread & fwrite

转自：http://www.cnblogs.com/lvpengms/archive/2011/05/01/2033779.html

This artical extracted from www.cplusplus.com.

fread
 

size_t fread ( void * ptr, size_t size, size_t count, FILE * stream );

Read block of data from stream
Reads an array of count elements, each one with a size of size bytes, from the stream and stores them in the block of memory specified by ptr.
The postion indicator of the stream is advanced by the total amount of bytes read.
The total amount of bytes read if successful is (size * count).

Parameters
ptr  　　Pointer to a block of memory with a minimum size of (size*count) bytes.
size 　　Size in bytes of each element to be read.
count 　　Number of elements, each one with a size of size bytes.　　
stream 　　Pointer to a FILE object that specifies an input stream.

Return Value
The total number of elements successfully read is returned as a size_t object, which is an integral data type.
If this number differs from the count parameter, either an error occured or the End Of File was reached.
You can use either ferror or feof to check whether an error happened or the End-of-File was reached.

/* fread example: read a complete file */#include <stdio.h>#include <stdlib.h>int main () {  FILE * pFile;  long lSize;  char * buffer;  size_t result;  pFile = fopen ( "myfile.bin" , "rb" );  if (pFile==NULL) {fputs ("File error",stderr); exit (1);}  // obtain file size:  fseek (pFile , 0 , SEEK_END);  lSize = ftell (pFile);  rewind (pFile);  // allocate memory to contain the whole file:  buffer = (char*) malloc (sizeof(char)*lSize);  if (buffer == NULL) {fputs ("Memory error",stderr); exit (2);}  // copy the file into the buffer:  result = fread (buffer,1,lSize,pFile);  if (result != lSize) {fputs ("Reading error",stderr); exit (3);}  /* the whole file is now loaded in the memory buffer. */  // terminate  fclose (pFile);  free (buffer);  return 0;}

fwrite

size_t fwrite ( const void * ptr, size_t size, size_t count, FILE * stream );

Write block of data to stream
Writes an array of count elements, each one with a size of size bytes, from the block of memory pointed by ptr to the current position in the stream.
The postion indicator of the stream is advanced by the total number of bytes written.
The total amount of bytes written is (size * count).

Parameters
ptr　　Pointer to the array of elements to be written.
size　　Size in bytes of each element to be written.
count　　Number of elements, each one with a size of size bytes.
stream　　Pointer to a FILE object that specifies an output stream.

Return Value
The total number of elements successfully written is returned as a size_t object, which is an integral data type.
If this number differs from the count parameter, it indicates an error.

/* fwrite example : write buffer */#include <stdio.h>int main (){  FILE * pFile;  char buffer[] = { 'x' , 'y' , 'z' };  pFile = fopen ( "myfile.bin" , "wb" );  fwrite (buffer , 1 , sizeof(buffer) , pFile );  fclose (pFile);  return 0;}

NOTE: the "wb" & "rb" is essential above!