A better way to print each word in a newline without using libraries (apart from stdio.h)?

Question

I'm trying to write a program that takes from the standard input stream a sentence, and based on the definition that a word is everything that is between "spaces"; "spaces" being the space character, tab character or newline character, so, for example, if the input stream is hey there this is some test, the output should be

hey
there
this
is
some
test

Here is my try:

#include <stdio.h>

#define TRUE 1
#define FALSE 0

#define IS_SPACE(c) ((c) == ' ' || (c) == '\t' || (c) == '\n')

int main() {

    for(int c, inWord = FALSE; (c = getchar()) != EOF;)
        if(!IS_SPACE(c)) {
            putchar(c);
            inWord = TRUE;
        }
        else if(inWord) {
            putchar('\n');
            inWord = FALSE;
        }

    return 0;
}

But I don't like this approach because I am manually entering TRUE and FALSE to inWord when it can be automatically be done by inWord = !IS_SPACE(c), but I don't know how to modify the code to make just one call to IS_SPACE without creating another temporal variable.

why don't just use [`isspace`](https://en.cppreference.com/w/c/string/byte/isspace)? — phuclv, Jul 15 '18 at 15:42
@phuclv I'm actually doing the examples of Ritchie and Kernighan's book and I want to use only the things that they introduce until that point, so that I master the basics. That's why I don't want libraries. — Garmekain, Jul 15 '18 at 15:48
You cannot do this without at least 1bit of *state*; to decide on the new state, the program needs to remember the previous state. (but: you could cheat by using recursion) — wildplasser, Jul 15 '18 at 15:56
... but actually the state *bit* is only needed to decide what needs to be output. — wildplasser, Jul 15 '18 at 16:11
K&R is so old that occasionally you'll find some odds [like this](https://stackoverflow.com/q/32652213/995714). Probably it's better to use a modern C book — phuclv, Jul 16 '18 at 02:00

score 1 · Answer 1 · edited Jul 15 '18 at 19:09

1

int  my_spaces[256] = { 0 };
my_spaces[' '] = my_spaces['\t'] = my_spaces['\n'] = 1;
#define MY_SPACE(c) (my_sapces[c])

This is the core of how isspace() and friends are often implemented but with bits for isspace(), isprint(), ....

Old answer before your edit: Look at strtok, though strtok_r is now my function of choice. Being built into C you can expect it to be optimized for the current implementation.

edited Jul 15 '18 at 19:09

answered Jul 15 '18 at 15:36

Gilbert

3,740
17
19

I actually don't want to use 'non-basic' libraries. I imported stdio because there is no way I could read the output any other way. – Garmekain Jul 15 '18 at 15:40
I edited the question title not to allow answers using string manipulation libraries. – Garmekain Jul 15 '18 at 15:41
See revised answer. And it should really use unsigned char. – Gilbert Jul 15 '18 at 16:05

score 1 · Answer 2 · answered Jul 15 '18 at 15:57

1

The bug is that it doesn't print the last '\n' if the text ends with nonspace. Or maybe it is a feature? I did not fix it.

As to your question, you may do

for(int c, inWord=FALSE; (c = getchar()) != EOF;) {
    if(!IS_SPACE(c))
        putchar(c);
    else if(inWord)
        putchar('\n');
    inword = !IS_SPACE(c);
}

or even

for(int c, bPrevInWord = FALSE; (c = getchar()) != EOF;) {
    int bInWord = !IS_SPACE(c);
    if(bInWord)
        putchar(c);
    else if(bPrevInWord)
        putchar('\n');
    bPrevInWord = bInWord;
}

answered Jul 15 '18 at 15:57

user31264

6,557
3
26
40

Not to be rude, but, your first example calls two times IS_SPACE, and your second one uses two temporal variables, which I explicitly excluded these. – Garmekain Jul 15 '18 at 16:00
2

Your action depends on whether `c` is nonspace AND whether the previous character is nonspace. So you need either two temporal variables or two calls to IS_SPACE, you probably cannot avoid this. (But, regarding two IS_SPACE calls, don't worry about efficiency, any compiler will optimize them away.) – user31264 Jul 15 '18 at 16:08
That's exactly what I've thought, but maybe anyone of you had a different point of view. Apparently not. Thanks. – Garmekain Jul 15 '18 at 16:13
1

Actually I tried the 3 versions(mine and the two yours) and the compiler does not optimize yours, in total my code takes 32 lines of asm, and yours 43 and 37 respectively. https://godbolt.org/g/c55JR8 – Garmekain Jul 30 '18 at 14:55

A better way to print each word in a newline without using libraries (apart from stdio.h)?

2 Answers2