Garbage Value in File after write

Question

I am making a log function which stores in a file.

int log_func(char* msg)
{
    int log_fd=0;
    ssize_t write_ret=0;
    int close_logfile_ret=0;
    time_t result;
    char error_msg[MAX_LOG_MSG_LEN]={' '};
    log_fd = open("/home/pi/log_client.txt", O_CREAT|O_APPEND|O_WRONLY);
    if(log_fd==-1)
    {
        printf("log failed !!----file open");
        exit(1);
    }

    result = time(NULL);
    snprintf(error_msg,MAX_LOG_MSG_LEN,"DALI_Server:%s:%s",asctime(localtime(&result)),msg);
    write_ret = write(log_fd,error_msg,sizeof(error_msg));

    if(write_ret == -1)
    {
        printf("log failed !!---- write");
        exit(1);
    }

    close_logfile_ret = close(log_fd);
    if(close_logfile_ret == -1)
    {
        printf("log failed !!---- close");
        exit(1);
    }
    return 0;
}

Here the array error_msg has been initialized to 'space'. but when i write less characters to it I get following result.

input: log_func("DALI Server Started");log_func("File open/create..."); output in file:

DALI_Server:Thu Jan 16 16:53:56 2014
:DALI Server started ^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@DALI_Server:Thu Jan 16 16:54:06 2014
File open/create...^@^@^@^@^@^@^@^@^@..

Why are the garbage characters coming.

You probably want `write_ret = write(log_fd,error_msg,strlen(error_msg));`. However, for this kind of I/O I'd suggest using functions `fopen`, `fprintf` and `fclose` instead of `open`, `write`, `close`. — Marian, Apr 09 '15 at 10:30
Any reason why you're using `open` instead of `fopen`? Because `open` (and `write` or `close`) are really low-level. `fopen` gives you a file pointer (`FILE *`), which makes for cleaner code, and boasts a much easier API — Elias Van Ootegem, Apr 09 '15 at 11:11

score 3 · Accepted Answer · answered Apr 09 '15 at 10:33

3

You write the whole error_msg array, even the contents after the string terminator. Instead you should use strlen to get the length of the string in the array, and only write that:

write_ret = write(log_fd, error_msg, strlen(error_msg));

answered Apr 09 '15 at 10:33

Some programmer dude

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but space character should have been there why ^@ – Haswell Apr 09 '15 at 10:55
1

@iand See [this old question and its answers](http://stackoverflow.com/questions/1065774/c-c-initialization-of-a-normal-array-with-one-default-value) – Some programmer dude Apr 09 '15 at 10:57

Garbage Value in File after write

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