Ficheros y estructuras

//compilacion g++ -std=c++11 -o NombreEjecutable NombreFuente.cpp

/* fread example: read an entire file */
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
using namespace std;

typedef struct alum {int clave;string nombre;}__ALUMNO__;

void escribe()
{

    __ALUMNO__ alumno;

    //FILE* fp = fopen( "alumnos.txt", "wb+" );

    FILE* fp = fopen( "alumnos.txt", "a+" );

    alumno.clave = 666;
    alumno.nombre = "Antonio";

    fwrite( &alumno, sizeof( __ALUMNO__ ), sizeof (alum)/8, fp );

    alumno.clave = 123;
    alumno.nombre = "Luis";

    fwrite( &alumno, sizeof( __ALUMNO__ ), sizeof (alum)/8, fp );

        alumno.clave = 789;
    alumno.nombre = "Anuska";

    fwrite( &alumno, sizeof( __ALUMNO__ ), sizeof (alum)/8, fp );


    fclose( fp );
}


int main () {
  FILE * pFile;
  long lSize;
  __ALUMNO__ * buffer, *buffer0;
  size_t result;

    escribe();

  pFile = fopen ( "alumnos.txt" , "r" );
  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 = (__ALUMNO__*) malloc (sizeof(__ALUMNO__)*lSize);
  if (buffer == NULL) {fputs ("Memory error",stderr); exit (2);}


  // copy the file into the buffer:

  result = fread (buffer,sizeof (alum)/8,lSize,pFile);
  if (result != lSize) {fputs ("Reading error",stderr); exit (3);}


    printf (" %d %s \n",(buffer)->clave,((buffer)->nombre).c_str());

  /* the whole file is now loaded in the memory buffer. */

  // terminate
  fclose (pFile);
 // printf (" %d %s \n",(buffer)->clave,((buffer)->nombre).c_str());

  free (buffer);
  return 0;
}