Questions about Strings

[Löwenherz]

hello, I have some simple questions For better understanding about Strings:

where does -> String Data Type comes from in freebasic like String, ZString, WString ?

a) it's c++ based and a string class? or b) in c the char type and creates
an array of characters to make a string? c) an own Data Type from quickbasic?

the freebasic String Functions of 'crt\string.bi' I cannot change the c runtime library Is fixed For using.

thanks, loewenherz

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' c
char greetings[] = "Hello World!";
printf("%s", greetings);

' c++
#include <string>

int main() {
    // char-Array mit 12 Elementen
    char a[] = "Hallo Welt!";

    // char-Array mit 12 Elementen
    std::string z = "Hallo Welt!";
}

freebasic

Code: Select all

' freebasic
' zstring example
Dim As ZString * 1000 buffer
Dim As ZString * 1000 b2

buffer = "1234" + Chr(0) + "5678"

Print Len(buffer), buffer
Print
For x As Integer = 0 To 8
   Print buffer[x],Chr(buffer[x])
Next

b2 = buffer
Print
Print Len(b2), b2
Print
For x As Integer = 0 To 8
   Print b2[x],Chr(b2[x])
Next

Sleep

' string example
Dim As String buffers
Dim As String b2a

buffers = "1234" + Chr(0) + "5678"

Print Len(buffers), buffers
Print
For xa As Integer = 0 To 8
   Print buffers[xa],Chr(buffers[xa])
Next

b2a = buffers
Print
Print Len(b2a), b2a
Print
For xa As Integer = 0 To 8
   Print b2a[xa],Chr(b2a[xa])
Next

Sleep

'

header c++

Code: Select all

<cstring> (string.h)
C Strings
This header file defines several functions to manipulate C strings and arrays.

Functions
Copying:
memcpy	Copy block of memory (function)
memmove	Move block of memory (function)
strcpy	Copy string (function)
strncpy	Copy characters from string (function)

Concatenation:
strcat	Concatenate strings (function)
strncat	Append characters from string (function)

Comparison:
memcmp	Compare two blocks of memory (function)
strcmp	Compare two strings (function)
strcoll	Compare two strings using locale (function)
strncmp	Compare characters of two strings (function)
strxfrm	Transform string using locale (function)

Searching:
memchr	Locate character in block of memory (function)
strchr	Locate first occurrence of character in string (function)
strcspn	Get span until character in string (function)
strpbrk	Locate characters in string (function)
strrchr	Locate last occurrence of character in string (function)
strspn	Get span of character set in string (function)
strstr	Locate substring (function)
strtok	Split string into tokens (function)

Other:
memset	Fill block of memory (function)
strerror	Get pointer to error message string (function)
strlen	Get string length (function)

Macros
NULL	Null pointer (macro)

Types
size_t	Unsigned integral type (type)

' ends

[Imortis]

hello, I have some simple questions For better understanding about Strings:

where does -> String Data Type comes from in freebasic like String, ZString, WString ?

a) it's c++ based and a string class? or b) in c the char type and creates
an array of characters to make a string? c) an own Data Type from quickbasic?

the freebasic String Functions of 'crt\string.bi' I cannot change the c runtime library Is fixed For using.

This is what the FB String type is internally, so it is basically B in your example above, but there is more to it than that so it is not 1-to-1.

Code: Select all

typedef struct _FBSTRING {
    char           *data;    /**< pointer to the real string data */
    ssize_t         len;     /**< String length. */
    ssize_t         size;    /**< Size of allocated memory block. */
} FBSTRING;

The 'crt\string.bi' file is not for FB strings. That is the C-Runtime (crt) String functions exposed to FB. So they are for C-style strings, which is basically what zstring is.

[Löwenherz]

Thank you imortis for clarification..

I Made a simple 'dummy test' for a Zstring Type

Only the Print Output doesn't Work and I am Sure thats Not working with my Idea

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' test demo: Define my ZString type
' my idea for Zstring Ptr with a type definition
'
Type ZStringy
    datas As ZString Ptr
End Type

' function to print a ZString
function PrintZString(zs As ZStringy) As ZString Ptr 'ByRef 
    If zs.datas <> 0 Then
        Print zs.datas
    Else
        Print "ZString is empty"
    End If
    Return @zs
End Function

Dim As ZString*14 myZString="Hello, World"

'PrintZString(cast(*myZString)) ' no

PrintZString(*myZstring) '' error 28 expected pointer

'Print myZstring 'ok but without using function printZstring()
sleep

[Imortis]

ZString manual

If you are using a zstring ptr, you need to use ALLOCATE to reserve the memory. If you use ZString * X, you don't need to allocate the memory, hence why the final print statement you have commented is the only one that works.

Can I ask what you are trying to accomplish with the type that contains only a zstring ptr?

[Löwenherz]

Hello imortis, thanks again For the link I know already This example,
I tried only To make a New 'Type ZString' defintion that's working
like a built-in ZString Data Type in freebasic, I thought it would be possible

Is there also Any typedef struct For _FBZSTRING { ... } FBZSTRING; ?

thanks

Code: Select all

'
typedef struct _FBZSTRING {
    char           *data;    /**< pointer to the real string data */
    ssize_t         len;     /**< String length. */
    ssize_t         size;    /**< Size of allocated memory block. */
} FBSTRING;

Code: Select all

' test demo2: Define my ZString type
' my idea for Zstring Ptr with a type definition
' 
Type ZStringy
    data1 As ZString*64 '? 
    datas As ZString Ptr '?
End Type


Declare Function PrintZString Alias "PrintZString" (ze As Zstringy) As ZString Ptr

' function to print a ZString
function PrintZString(zs As ZStringy) As ZString Ptr 'ByRef 
    If zs.datas <> 0 Then
        Print zs.datas
    Else
        Print "ZString is empty"
    End If
    Return @zs
End Function

'Dim As ZString*14 myZString="Hello, World"

Dim As ZString Ptr myZstring 
myZstring = Allocate( 14 )
*myZstring="Hello, World"
Print *myZstring 
Print Len(*myZstring) '12
Print SizeOf(*myZstring) '1

'PrintZString(cast(*myZString)) ' no

' error next line
PrintZString(@myZstring) '' error 58 type mismatch at parameter 1 (zs)

' Print *myZstring 'ok but without using sub printZstring()
Sleep

[fxm]

Previously I wrote an example of an Auto-Sized Zstring Object, but the code is not as trivial as you might expect.

[Löwenherz]

hello fxm, thanks For you link And your example, looks interesting I will study
your 'Type ZstringObject Extends ZString' example looks good.

can you Do me a favour and check my last little code example what's wrong here
With the ZString Pointer? it's just a test nothing more..
I would like To get a result For PrintZString() Function at the End

thanks, loewenherz

Code: Select all

' test demo2: Define my ZString type
' my idea for Zstring Ptr with a type definition
' 
Type ZStringy
    data1 As ZString*64 '? 
    datas As ZString Ptr '?
End Type


Declare Function PrintZString Alias "PrintZString" (ze As Zstringy) As ZString Ptr

' function to print a ZString
function PrintZString(zs As ZStringy) As ZString Ptr 'ByRef 
    If zs.datas <> 0 Then
        Print zs.datas
    Else
        Print "ZString is empty"
    End If
    Return @zs ' pointer problem
End Function

'Dim As ZString*14 myZString="Hello, World"

Dim As ZString Ptr myZstring 
myZstring = Allocate( 14 )
*myZstring="Hello, World"
Print *myZstring 
Print Len(*myZstring) '12
Print SizeOf(*myZstring) '1

' error next line, why ???
PrintZString(@myZstring) '' error 58 type mismatch at parameter 1 (zs)

' Print *myZstring 'ok but without using sub printZstring()
Sleep

[fxm]

Two unsafe solutions to make this twisted code work:

Code: Select all

' test demo2: Define my ZString type
' my idea for Zstring Ptr with a type definition
' 
Type ZStringy
    data1 As ZString*64 '? 
End Type


Declare Function PrintZString Alias "PrintZString" (ze As Zstringy) As ZString Ptr

' function to print a ZString
function PrintZString(zs As ZStringy) As ZString Ptr 'ByRef 
    If Len(zs.data1) > 0 Then
        Print zs.data1
    Else
        Print "ZString is empty"
    End If
    Return @zs.data1 ' pointer problem
End Function

Dim As ZString Ptr myZstring 
myZstring = Allocate( 14 )
*myZstring="Hello, World"
Print *myZstring 
Print Len(*myZstring) '12
Print SizeOf(*myZstring) '1

' error next line, why ???
PrintZString(*Cptr(ZStringy Ptr, myZstring)) '' error 58 type mismatch at parameter 1 (zs)

' Print *myZstring 'ok but without using sub printZstring()
Sleep

or:

Code: Select all

' test demo2: Define my ZString type
' my idea for Zstring Ptr with a type definition
' 
Type ZStringy
    datas As ZString Ptr '?
End Type


Declare Function PrintZString Alias "PrintZString" (ze As Zstringy) As ZString Ptr

' function to print a ZString
function PrintZString(zs As ZStringy) As ZString Ptr 'ByRef 
    If zs.datas <> 0 Then
        Print *zs.datas
    Else
        Print "ZString is empty"
    End If
    Return zs.datas ' pointer problem
End Function

Dim As ZString Ptr myZstring 
myZstring = Allocate( 14 )
*myZstring="Hello, World"
Print *myZstring 
Print Len(*myZstring) '12
Print SizeOf(*myZstring) '1

' error next line, why ???
PrintZString(*Cptr(ZStringy Ptr, @myZstring)) '' error 58 type mismatch at parameter 1 (zs)

' Print *myZstring 'ok but without using sub printZstring()
Sleep

[fxm]

Otherwise, two other more safe codes:

Code: Select all

' test demo2: Define my ZString type
' my idea for Zstring Ptr with a type definition
' 
Type ZStringy
    data1 As ZString*64 '? 
End Type


Declare Function PrintZString Alias "PrintZString" (ze As Zstringy) As ZString Ptr

' function to print a ZString
function PrintZString(zs As ZStringy) As ZString Ptr 'ByRef 
    If Len(zs.data1) > 0 Then
        Print zs.data1
    Else
        Print "ZString is empty"
    End If
    Return @zs.data1 ' pointer problem
End Function

Dim As ZStringy myZstring 
myZstring=Type("Hello, World")
Print myZstring.data1 
Print Len(myZstring.data1) '12
Print SizeOf(myZstring.data1) '1

' error next line, why ???
PrintZString(myZstring) '' error 58 type mismatch at parameter 1 (zs)

' Print *myZstring 'ok but without using sub printZstring()
Sleep

or:

Code: Select all

' test demo2: Define my ZString type
' my idea for Zstring Ptr with a type definition
' 
Type ZStringy
    datas As ZString Ptr '?
End Type


Declare Function PrintZString Alias "PrintZString" (ze As Zstringy) As ZString Ptr

' function to print a ZString
function PrintZString(zs As ZStringy) As ZString Ptr 'ByRef 
    If zs.datas <> 0 Then
        Print *zs.datas
    Else
        Print "ZString is empty"
    End If
    Return zs.datas ' pointer problem
End Function

Dim As ZStringy myZstring 
myZstring.datas = CAllocate( 14 )
*myZstring.datas="Hello, World"
Print *myZstring.datas 
Print Len(*myZstring.datas) '12
Print SizeOf(*myZstring.datas) '1

' error next line, why ???
PrintZString(myZstring) '' error 58 type mismatch at parameter 1 (zs)

' Print *myZstring 'ok but without using sub printZstring()
Sleep
Deallocate(myZstring.datas)

[Löwenherz]

hello fxm, many thanks For your corrections and examples, fast replies, I have learned new things again..
a) PrintZString(*CPtr(Zstringy PTR, myZstring)) with *CPtr() b) And Callocate() were New functions For me..
c) And Type() as myZstring=Type("Hello, World").

I have done some simple ZString Ptr examples below And took corrections
but I don't know if anybody else already has done it before

loewenherz

Code: Select all

' I have done some corrections of zstring ptr examples I have found
' freebasic, 17-06-2025, loewenherz
'
' --- example 1 ok
Dim As ZString Ptr abc = @"Hello" 

If ( *abc <> "" ) Then Print *abc
If Len( *abc ) Then Print *abc
Print abc '4223020
Print Len(abc) '4
Print SizeOf(abc) '4
Sleep

' --- example 2 corrections below
' not good
' Dim As Zstring * 1 z
' Dim As String s

' If z Then Print z 'no, error 24: Invalid data types, found 'Then'
' If s Then Print s 'no, error 24: Invalid data types, found 'Then'

'Sleep

' good way
Dim As Zstring * 1 zu
Dim As String su

If ( zu <> "") Then Print zu 'go
If ( su <> "") Then Print su 'go
Print "ok"
Sleep


' --- example 3 corrections below 
Dim As Zstring * 14 ze = "FreeBASIC2025"
Dim As Zstring Ptr pz = @ze

Dim As String sx = "FreeBASIC2025"
Dim As String Ptr ps = @sx

' not good
'If z Then Print z  '' error 24: Invalid data types
'If s Then Print s  '' error 24: Invalid data types

' good
If ( ze <> "" ) Then Print ze
If ( sx <> "" ) Then Print sx

If *pz Then Print ze  '' go
'If  *ps Then Print sx ' no, error 24: Invalid data types
If  ps Then Print sx  '' corrected version
Print "ok2"

Sleep

[fxm]

Note:
- The value of the 'Sizeof()' function for a Zstring variable is well-defined only if the Zstring variable has been explicitly sized at its declaration level (by '... As Zstring * N').
- Otherwise, the default value of 'Sizeof()' for a Zstring variable is '1'.
- Only the value of the 'Len()' function is always well-defined.
Example:

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Dim As Zstring * 10 z = "Hello"
Print Len(z)
Print Sizeof(z)
Print

Dim As Zstring Ptr pz = @"Hello"
Print Len(*pz)
Print Sizeof(*pz)

Sleep