ascii_copy.c

/**
 * This script implements a very simple string copy that is the same length
 * or less bytes. The copied string only contains printable characters.
 */

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

// Duplicate the string src without any non-printable characters.
char* strcpy_pc(const char* src)
{
    assert(src != NULL);

    char* dst        = NULL;
    int   src_offset = 0;
    int   dst_offset = 0;

    // To clean the string, we'll first allocate all the required memory:
    dst = malloc(sizeof(char) * strlen(src) + 1);
    assert(dst != NULL);

    // Next, loop over each character and if it's permitted, add it:
    while (true)
    {
        // If we run over a null byte - copy it and exit.
        if (src[src_offset] == 0)
        {
            dst[dst_offset] = 0;

            // We can now resize to the memory that's needed.
            dst = realloc(dst, sizeof(char) * (strlen(dst) + 1));
            assert(dst != NULL);

            return dst;
        }

        // Skip DEL byte (0x7F) and anything below 31 (0x1F).
        if (src[src_offset] < 32 || src[src_offset] == 127)
        {
            src_offset++;
            continue;
        }

        // For all remaining bytes, copy them.
        dst[dst_offset] = src[src_offset];
        dst_offset++;
        src_offset++;
    }
}

//
// Tests
//

#include "../picotest/lib/framework.h"

IT_SHOULD(do_nothing_with_an_empty_string, {
    char* dst = strcpy_pc("");

    ASSERT_STR_EQ("", dst);
})

IT_SHOULD(return_identical_string_with_no_printable_characters, {
    char* src = "hello";
    char* dst = strcpy_pc(src);

    ASSERT_STR_EQ(src, dst);
})

IT_SHOULD(remove_non_printable_characters_at_the_end, {
    char* src = "hello\x01";
    char* dst = strcpy_pc(src);

    ASSERT_STR_EQ("hello", dst);
})

IT_SHOULD(remove_non_printable_characters_anywhere_in_the_string, {
    char* src = "h\ae\x01llo\x01";
    char* dst = strcpy_pc(src);

    ASSERT_STR_EQ("hello", dst);
})

int main()
{
    BEGIN_TESTING;

    RUN_TEST(do_nothing_with_an_empty_string);
    RUN_TEST(return_identical_string_with_no_printable_characters);
    RUN_TEST(remove_non_printable_characters_at_the_end);
    RUN_TEST(remove_non_printable_characters_anywhere_in_the_string);

    CONCLUDE_TESTING;
}