8.3 Character, String, and Line I/O

C also gives you smaller I/O tools for individual characters and whole strings. These work with the console streams stdin and stdout, or with file streams opened by fopen().

Function	Stream	What it does	Important detail
`getchar()`	`stdin`	Reads one character	Returns `int`, so it can return `EOF`
`putchar(ch)`	`stdout`	Writes one character	Sends exactly one character
`fgetc(fp)`	file stream	Reads one character from a file	Returns `int` for `EOF`
`fputc(ch, fp)`	file stream	Writes one character to a file	Useful for character filters
`puts(text)`	`stdout`	Writes a string	Adds a newline
`fputs(text, fp)`	file stream	Writes a string	Does not add a newline
`fgets(buf, size, stream)`	any input stream	Reads at most `size - 1` characters	Keeps the buffer inside its limit
`gets(buf)`	`stdin`	Old unsafe line input	Do not use it; it has no size limit

Single-character console I/O often looks like this:

int ch;

while ((ch = getchar()) != EOF) {
    putchar(ch);
}

The same pattern can transform a file one character at a time:

FILE *in = fopen("raw.txt", "r");
FILE *out = fopen("clean.txt", "w");

int ch;
while ((ch = fgetc(in)) != EOF) {
    if (ch == '\t') {
        fputc(' ', out);
    } else {
        fputc(ch, out);
    }
}

fclose(out);
fclose(in);

For strings and lines, prefer fgets() because it receives the buffer size:

char line[80];

while (fgets(line, sizeof(line), stdin) != NULL) {
    fputs(line, stdout);
}

You may see gets(buffer) in old material, but it cannot know how large buffer is. It can write past the end of the array, so modern C removed it. Use fgets() instead.

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