/*
 * This program demonstrates how setvbuf can specify the kind
 * of buffering used for a file stream.  
 *
 * Side-Effects: Output is written to a file "setvbuf.out"
 *               (previous contents erased)
 * 
 * Commands used: fflush, sprintf, fprintf, fopen, fclose, setvbuf, putc
 */ 

#include <stdio.h>
#include <stdlib.h>  /* system()  needs this */
#include <ctype.h>   /* toupper() needs this */

#define MAX_LINE 80

main()
{
    char aString [MAX_LINE];
    int  length = 0;
    FILE *fp1 = NULL;
    FILE *fp2 = NULL;
    int  i; 
 
    sprintf(aString, "abcdefghijklmnopqrstuvwxyz\n");
    length = strlen(aString);

    /* 
     * remove any setvbuf.out files lingering around from previous
     * executions (see p. 221)
     */
    system("rm -f setvbuf.out");

    if ( (fp1 = fopen("setvbuf.out", "a+")) == NULL )
    {
        fprintf(stderr, "Error.  Couldn't open fp1 file with a+\n");
        exit(1);
    }

    if ( (fp2 = fopen("setvbuf.out", "a+")) == NULL )
    {
        fprintf(stderr, "Error.  Couldn't open fp2 file with a+\n");
        exit(1);
    }

    /* 
     * First test:
     *     set fp1 to be line buffered
     *     set fp2 to be unbuffered
     */
    setvbuf(fp1, NULL, _IOLBF, NULL);
    setvbuf(fp2, NULL, _IONBF, NULL);

    fprintf(fp1, "Test #1.  Lowercase is line buffered, uppercase is unbuffered:\n");
    fprintf(fp1, "--------------------------------------------------------------\n\n");
    fflush(fp1);

    for (i = 0; i < length; i++)
    {
        putc (aString[i], fp1);
        putc (toupper(aString[i]), fp2);
    }

    fclose(fp1);
    fclose(fp2);

    /*
     * Re-opening files so that the setvbuf gets executed before any operation 
     * is performed on the stream
     */
    if ( (fp1 = fopen("setvbuf.out", "a+")) == NULL )
    {
        fprintf(stderr, "Error.  Couldn't RE-open fp1 file with a+\n");
        exit(1);
    }

    if ( (fp2 = fopen("setvbuf.out", "a+")) == NULL )
    {
        fprintf(stderr, "Error.  Couldn't RE-open fp2 file with a+\n");
        exit(1);
    }

    /* 
     * Second test:
     *     set fp1 to be unbuffered 
     *     set fp2 to be unbuffered 
     */
    setvbuf(fp1, NULL, _IONBF, NULL);
    setvbuf(fp2, NULL, _IONBF, NULL);

    fprintf(fp1, "\nTest #2.  Both upper and lower case are unbuffered:\n");
    fprintf(fp1, "--------------------------------------------------------------\n\n");
    fflush(fp1);

    for (i = 0; i < length; i++)
    {
        putc (aString[i], fp1);
        putc (toupper(aString[i]), fp2);
    }
}