MID$

Returns a number of characters from a given starting position of a string

Implemented by: altair8K, Applesoft, CBM, msatari, level2, trscolor, colormc, BBC, GWBASIC, bwbasic, bw32, ABasiC, QBasic, VBDOS, Gambas, minibasicmm, minibasicjs

With variations: atxl (position 0 causes error), trsdisk (can receive a string), level3 (can rceive a string), MSX (can be assigned a value, for substitution)

Also written as:

The basic syntax is:

stringvar$ = MID$ (str, startpos, n)

where str is the source string, startpos is the position of the first character of the desired substring (starting from left), and n is the number of characters to extract.

The following example is from the Atari Microsoft BASIC manual:

100 A$ = "GETTHEMIDDLE"
110 PRINT MID(A$,4,3)

As expected, the numerical arguments to MID$ may vary a lot:

• startpos begins from 0 in msx
• startpos begins from 1 in msatari
• Values for startpos and n must be in the 8-bit range of 0 to 255 for most 8-bit BASICs. Strings could not have more than 255 characters in most of them anyway.

n is optional and, if ommited, all characters from startpos to the end of str are returned − this stands true for msx.

If n from startpos surpasses the end of str, most BASICs will simply return all characters from startpos to the end of str.

Watch out for differences in the effects of a negative value for n or startpos.

Some BASICs, especially Microsoft-based ones such as MSX BASIC and TRS-80 Level III BASIC, allow a strange syntax where MID$ receives a string value, which will replace the substring found by the function, effectively altering the source string str. An example:

10 A$ = "ABC"
20 MID$(A$, 1, 1) = "Basic!"
30 PRINT A$

In the Microsoft realm, the keyword first appeared in the 8k version of Altair BASIC.

• LEFT$ and RIGHT$
• INSTR as a way to find the first character of a substring