INSTR() Function Performs ASCII Compare and Is Case Sensitive

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Article ID: 44799 - View products that this article applies to.
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The INSTR function (provided in all Microsoft BASICs) compares the ASCII values of the search string with the ASCII values of the string to be searched, and is, therefore, case sensitive. For example, when INSTR compares "AB" with "Ab", INSTR returns 0 (zero) because the strings are different.

This information applies to the following products:

  1. Microsoft QuickBASIC Version 1.00 for the Apple Macintosh
  2. Microsoft BASIC Compiler Version 1.00 for the Apple Macintosh
  3. Microsoft BASIC Interpreter Versions 1.00, 1.01, 2.00, 2.10, and 3.00 for the Apple Macintosh
  4. Microsoft QuickBASIC Compiler Versions 1.00, 1.01, 1.02, 2.00, 2.01, 3.00, 4.00, 4.00b, and 4.50 for the IBM PC
  5. Microsoft BASIC Compiler Versions 5.35 and 5.36 for MS-DOS
  6. Microsoft BASIC Compiler Versions 6.00, and 6.00b for MS OS/2 and MS-DOS
  7. Microsoft BASIC Profesional Development System 7.00 for MS-DOS and MS OS/2
  8. Microsoft GW-BASIC Interpreter Versions 3.20, 3.22, and 3.23


The INSTR function returns the character position of the first occurrence of a string in another string. The syntax for INSTR is as follows
INSTR ( [Start,] string1, string2 )
where the variables refer to the following:
   Variable  Description

   Start     The [optional] character location to begin searching in

   string1   The character string to be searched

   string2   The character string to be searched for
The values returned by the INSTR function are as follows:
   Value     Description

   n         Refers to the character position of string2 in string1.

   0         string2 was not found in string1.

   0         string1 is a null string ("").

   0         The value for Start is greater than the length of string1.
If string2 is a null string (""), then INSTR returns the value of 1 unless a Start argument was specified, in which case it returns a value equal to Start.

For more information about the INSTR function, please consult your BASIC language reference manual.

Code Example

   PRINT INSTR("ABCDEF","D")   ' Found in column 4.
   PRINT INSTR("ABCDEF","d")   ' Not found, since case differs


Article ID: 44799 - Last Review: November 21, 2006 - Revision: 1.3
  • Microsoft QuickBasic Compiler for Macintosh 1.0
  • Microsoft BASIC Compiler 6.0b
  • Microsoft BASIC Interpreter 1.0
  • Microsoft BASIC Interpreter 1.01 for Macintosh
  • Microsoft BASIC Interpreter 2.0
  • Microsoft BASIC Interpreter 2.1 for Macintosh
  • Microsoft BASIC Interpreter 3.0 for Macintosh
  • Microsoft QuickBasic 1.0
  • Microsoft QuickBasic 1.01
  • Microsoft QuickBasic 1.02
  • Microsoft QuickBASIC 1.0b
  • Microsoft QuickBASIC 1.0b
  • Microsoft QuickBasic 2.0
  • Microsoft QuickBasic 2.01
  • Microsoft QuickBasic 3.0
  • Microsoft QuickBasic 4.0
  • Microsoft QuickBASIC 4.0b
  • Microsoft QuickBasic 4.5 for MS-DOS
  • Microsoft BASIC Compiler 6.0b
  • Microsoft BASIC Compiler 6.0
  • Microsoft BASIC Compiler 6.0b
  • Microsoft BASIC Professional Development System 7.0
  • Microsoft GW-BASIC Interpreter 1.0
Retired KB Content Disclaimer
This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.

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