Example of a function that does not like overlapping buffers

prune-spaces.c

#include <assert.h>
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>

#define BUF_SIZE 256

/* source and destination buffers MUST NOT overlap */
char *
prune_spaces(char * dst, size_t dst_len, const char * src)
{
    char * const original_destination = dst;

    assert(src != NULL);
    assert(dst != NULL);
    assert(dst_len > 0);

    for (;;) {
        if (dst_len == 1 || *src == '\0') {
            *dst = '\0';
            break;
        }
        if (!isspace(*src)) {
            *dst = *src;
            dst++;
            dst_len--;
        }
        src++;
    }


    return original_destination;
}

int
main(int argc, char *argv[])
{
    (void) argc;
    (void) argv;

    char read_buf[BUF_SIZE];
    char prune_buf[BUF_SIZE];

    for (;;) {
        printf("> ");
        fflush(stdout);
        fgets(read_buf, BUF_SIZE, stdin);
        printf("%s\n", prune_spaces(prune_buf, BUF_SIZE, read_buf));
    }

    return 0;
}