php upper and lowercase without built in function

Question

Hey guys i want to convert a string from lowercase to uppercase and vice versa without using any built in functions strtoupper or strtolower in php, can anyone help me please.

edit: I can use some other functions to do the job, like substr(), ord(), chr(), strlen(), str_replace.

This was my first question here so could not specify what i needed in best way. I was given task to do the job in these mentioned functions without use of arrays either.

...next time i will be careful.

could you explain why you don't want to use built in functions? — Marko D, Feb 27 '13 at 11:49
toggle the 6th bit is perhaps the best solution. The whole question is absurd, trivial or academic. ... voting down — NappingRabbit, Feb 27 '13 at 12:04
What have you tried?What errors have you found?What research have you done?Why would you not want to use PHP built in functions?On the whole not a good question. Downvoted — david strachan, Feb 27 '13 at 12:13

score 3 · Answer 1 · answered Feb 27 '13 at 12:07

the c functions look like:

PHPAPI char *php_strtoupper(char *s, size_t len)
{
    unsigned char *c, *e;

    c = (unsigned char *)s;
    e = (unsigned char *)c+len;

    while (c < e) {
        *c = toupper(*c);
        c++;
    }
    return s;
}

PHPAPI char *php_strtolower(char *s, size_t len)
{
    unsigned char *c, *e;

    c = (unsigned char *)s;
    e = c+len;

    while (c < e) {
        *c = tolower(*c);
        c++;
    }
    return s;
}

but also these functions use tolower and toupper from ctype.h C library! look at the souce here

score 2 · Accepted Answer · answered Feb 27 '13 at 11:55

2

function myStrToLower($string) {
    $from = range('A','Z');
    $to = range('a','z');
    return str_replace($from, $to, $string);
}

function myStrToUpper($string) {
    $from = range('a','z');
    $to = range('A','Z');
    return str_replace($from, $to, $string);
}

answered Feb 27 '13 at 11:55

Mark Baker

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`range` and `str_replace` are built-in functions...Edit: OK, OP edited his question – Passerby Feb 27 '13 at 11:56

NappingRabbit · Answer 3 · 2013-02-27T12:01:22.260

while I can not imagine why you would want to do this; you may consider making an array matching the lowercase to the uppercase of each letter. Then for every character in the string, find it in this array and return the value. (or the key if you are going the other direction).

While built in functions have overhead, I think this method will incur more overhead still.

EDIT: alternatively, you could convert each character to ascii then check the range to see if it is upper or lowercase. Then add or subtract 32 (dec) to change to the other case.

Andreas Hagen · Answer 4 · 2013-02-27T12:14:49.647

One possible implementation (if you allow for str_split) would be:

function myToLowerCase( $str )
{
    static $charMap = array(
        'A' => 'a', 'B' => 'b', 'C' => 'c', 'D' => 'd', 'E' => 'e', 'F' => 'f',
        'G' => 'g', 'H' => 'h', 'I' => 'i', 'J' => 'j', 'K' => 'k', 'L' => 'l',
        'M' => 'm', 'N' => 'n', 'O' => 'o', 'P' => 'p', 'Q' => 'q', 'R' => 'r',
        'S' => 's', 'T' => 't', 'U' => 'u', 'V' => 'v', 'W' => 'w', 'X' => 'x',
        'Y' => 'y', 'Z' => 'z',
    );
    $chars = str_split( $str );
    $result = '';

    for ( $i = 0; $i < count( $chars ); $i++ )
    {
        if ( isset( $charMap[$chars[$i]] ) )
        {
            $result .= $charMap[$chars[$i]];
        }
        else
        {
            $result .= $chars[$i];
        }
    }

    return $result;
}

The uppercase equivalent should be obvious from looking at the example.

php upper and lowercase without built in function

4 Answers4