Thread: help me understand setvbuf function

  1. #1
    Registered User
    Join Date
    Sep 2008
    Posts
    40

    help me understand setvbuf function

    Code:
    #include <stdio.h>
    
    #include <stdlib.h>
    
    #include <string.h>
    
    #define BUFSIZE 1024
    
    #define SLEN 81
    
    void append(FILE *source, FILE *dest);
    
    
    
    int main(void)
    
    {
    
        FILE *fa, *fs;// fa for append file, fs for source file
    
        int files = 0;  // number of files appended
    
        char file_app[SLEN];  // name of append file
    
        char file_src[SLEN];  // name of source file
    
        puts("Enter name of destination file:");
    
        gets(file_app);
    
        if ((fa = fopen(file_app, "a")) == NULL)
    
        {
    
            fprintf(stderr, "Can't open %s\n", file_app);
    
            exit(2);
    
        }
    
        if (setvbuf(fa, NULL, _IOFBF, BUFSIZE) != 0)
    
        {
    
            fputs("Can't create output buffer\n", stderr);
    
            exit(3);
    
        }
    
        puts("Enter name of first source file (empty line to quit):");
    
        while (gets(file_src) && file_src[0] != '\0')
    
        {
    
            if (strcmp(file_src, file_app) == 0)
    
                fputs("Can't append file to itself\n",stderr);
    
            else if ((fs = fopen(file_src, "r")) == NULL)
    
                fprintf(stderr, "Can't open %s\n", file_src);
    
            else
    
            {
    
                if (setvbuf(fs, NULL, _IOFBF, BUFSIZE) != 0)
    
                {
    
                    fputs("Can't create input buffer\n",stderr);
    
                    continue;
    
                }
    
                append(fs, fa);
    
                if (ferror(fs) != 0)
    
                    fprintf(stderr,"Error in reading file %s.\n",
    
                            file_src);
    
                if (ferror(fa) != 0)
    
                    fprintf(stderr,"Error in writing file %s.\n",
    
                            file_app);
    
                fclose(fs);
    
                files++;
    
                printf("File %s appended.\n", file_src);
    
                puts("Next file (empty line to quit):");
    
            }
    
        }
    
        printf("Done. %d files appended.\n", files);
    
        fclose(fa);
    
    
    
        return 0;
    
    }
    
    
    
    void append(FILE *source, FILE *dest)
    
    {
    
        size_t bytes;
    
        static char temp[BUFSIZE]; // allocate once
    
        while ((bytes = fread(temp,sizeof(char),BUFSIZE,source)) > 0)
    
            fwrite(temp, sizeof (char), bytes, dest);
    
    }
    can someone explain to me how the setvbuf() function works? and also the append function in this sample program thanks..

  2. #2
    Kernel hacker
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    Farncombe, Surrey, England
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    15,677
    Read:
    http://linux.die.net/man/3/setvbuf

    If you still have questions, please ask.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
    and the hat of int overfl Salem's Avatar
    Join Date
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    The edge of the known universe
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    Also read the FAQ on why gets() is bad news.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

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