Operator Strptr (String Pointer)operator

Returns the address of a string's character data.

Syntax

Declare Operator StrPtr ( ByRef lhs As String ) As ZString Ptr

Declare Operator StrPtr ( ByRef lhs As WString ) As WString Ptr

Parameters

Return value

Returns a ZString/WString Ptr to a string/wstring's character data (null value in case of empty string).

Description

This operator returns a ZString/WString Ptr that points to the beginning of a string/wstring's character data. Operator Strptr is the proper method for acquiring the address of a string's character data.
In case of empty String (only for variable length strings), Operator Strptr returns a null pointer.

The related Operator Varptr (Variable Pointer) and Operator @ (Address Of), when used with a String, return the address of the internal string descriptor.
When a variable length string is modified, the address of its descriptor remains always the same, but the the string's character data address (returned by Operator Strptr) may change (like any allocated memory that must be reallocated).
When a fixed length string is modified, the string's character data address (returned by Operator Strptr) is unchanged.

Note: For a variable length string, the operator returns a ZString Const Ptr (because returning by reference the string's characters pointer set in the string descriptor, this one is to be considered as read only). If the keyword Var is used to declare/initialize a user pointer from Operator Strptr, this user pointer is also defined as read only (it can not be modified further).

Warning: Since fbc version 1.20.0, dereferencing a zstring pointer to a fixed-length string of STRING*N type (which no longer has an additional terminal null character as before) can lead to an extension of the string by some pollution, or even an outright crash.

Remarks

Usage


result = StrPtr ( lhs )


Differences from QB

• New to FreeBASIC, but does exactly the same thing as SAdd
  
  

See also

• SAdd
  
• VarPtr
  
• ProcPtr
  
• Pointers
  
  

Example

'' This example uses Strptr to demonstrate using pointers with strings

Dim myString As String

Dim toMyStringDesc As Any Ptr

Dim toMyString As ZString Ptr



'' Note that using standard VARPTR notation will return a pointer to the

'' descriptor, not the string data itself

myString = "Improper method for Strings"

toMyStringDesc = @myString

Print myString

Print Hex( toMyStringDesc )

Print



'' However, using Strptr returns the proper pointer

myString = "Hello World Examples Are Silly"

toMyString = StrPtr(myString)

Print myString

Print *toMyString

Print



'' And the pointer acts like pointers to other types

myString = "MyString has now changed"

Print myString

Print *toMyString

Print

Reference

• Documented in KeyPgOpStrptr.html