C string disappears along with newline

Question

I'm new to C and stackoverflow, so pardon me if my question is silly or a duplicate.

So i tried to read some lines of string (and integers) from a .txt files and store it into an array of tuples. The strings read from the file seems to contain '\n' everytime, so i use strcspn() to remove it.

    FILE* f = fopen("board.txt","r");
    int x;
    size_t size = 30;
    char *buffer;
    for (i=1;i<=32;i++)
        {
            buffer = (char *)malloc(size);
            x = getline(&buffer,&size,f);
            buffer[strcspn(buffer,"\n")] = 0;
            A[i].name = buffer;
            buffer = (char *)malloc(size);
            x = getline(&buffer,&size,f);
            buffer[strcspn(buffer,"\n")] = 0;
            A[i].type = buffer;
            buffer = (char *)malloc(size);
            x = getline(&buffer,&size,f);
            A[i].price = atoi(buffer);
        }
    for (i=1;i<=32;i++)
        printf("%s ",A[i].name);
    for (i=1;i<=32;i++)
        printf("%s ",A[i].type);

However, when i tried the code above, the printf failed to print anything. But then when i tried to use \n in the printf ( printf("%s\n",A[i].type); ) it worked just fine. It seems like the strings completely disappear when i remove the "\n", and then come back only when i put '\n' as i print it.

Can someone explain what is wrong in the code? Or is it a library problem? Thank you in advance.

Edit : So to explain it a little further, i need those string (name and type) to be printed into 'boxes' to form a kind of board game, so i think bringing newline would cause a lot of trouble later on.

Possible duplicate of [Why does printf not flush after the call unless a newline is in the format string?](http://stackoverflow.com/questions/1716296/why-does-printf-not-flush-after-the-call-unless-a-newline-is-in-the-format-strin) — R Nar, Nov 13 '15 at 00:39
nothing in particular...it actually have its own id later on, so to avoid confusing myself i skipped the 0 — SimpliCty, Nov 13 '15 at 00:52

score 2 · Accepted Answer · answered Nov 13 '15 at 00:39

2

This is the correct behavior. The '\n' causes the OS to flush the buffer used for prints, so that it appears on stdout. Without a '\n' the OS isn't forced to write your print to stdout yet.

answered Nov 13 '15 at 00:39

TheoretiCAL

19,461
8
43
65

Thanks for the explanation... but is there any way to actually make it like a usual string, printable without the newline? – SimpliCty Nov 13 '15 at 00:50
I mean how can i actually return to unbuffered output mode or something? Because later on i will insert the array into a list and print it part by part, and i still don't really get a grasp on the buffering printing. Sorry for the silly question. – SimpliCty Nov 13 '15 at 02:15

score 0 · Answer 2 · answered Nov 13 '15 at 01:55

0

printf belongs to the Standard I/O library, it is a line buffered function. So when this function is called, it stores characters in a buffer and the only way to get the output (to stdout) is to flush with a newline character. This is the way it was designed so as to maintain a minimal number of system calls as possible.

Try eliminating this,

 buffer[strcspn(buffer,"\n")] = 0;

answered Nov 13 '15 at 01:55

jarr

102
2
7

yeah, but the problem is i actually need that string without the newline, and i still don't really understand how you can output that in a simple way.. – SimpliCty Nov 13 '15 at 02:18
You can use `setvbuf()` with mode to `_IONBUF`. It makes the `printf()` function to not wait until its buffer is full before flushing. This makes `printf()` immediately call `write()`. – jarr Nov 13 '15 at 18:43

C string disappears along with newline

2 Answers2