B4R Question size_t* to global variable

KMatle · Jan 13, 2023

I'm still a noob in C

I have

C:

size_t olen = 0;

and later it is used as a pointer like &olen

As far as I know this is a pointer to an unsigned int variable.

Via b4r_main::_encrypted_len = olen; all works but I want to drop that extra step and use/cast the variable directly to a B4R variable. I tried (uint8_t*) and other things but it didn't work.

Could someone help me out here? Thanks.

candide · Jan 13, 2023

to store a byte in B4R in a variable accessible in c++ by pointer for read/write: i think it can be done with ArrayByte
in B4R:
Dim datx(1) as byte
datx(0) = 111
in wrapper c++
uint8_t * varx = datx->data;
xxx = &varx[0];
===> xxx will be a pointer to your variable in B4R and a modification under c++ will change B4R variable value

i am not sure it is what you want !

KMatle · Jan 15, 2023

Thanks. Will try this.

candide · Jan 15, 2023

if you are using inline C, you can find several examples in this forum to modify a global variable B4R from inline C

Inline C / C++

As in the other B4X tools you can embed C or C++ code in the project. Example: Sub Process_Globals Public Serial1 As Serial Private Result, N1, N2 As Int 'ignore End Sub Private Sub AppStart Serial1.Initialize(115200) Log("AppStart") N1 = 10 N2 = 20 RunNative("Add", Null)...

www.b4x.com

KMatle · Jan 18, 2023

I wasn't precise enough.

In inline C I use this function which returns &olen (which is size_t)

C:

mbedtls_pk_encrypt( &pk, (uint8_t*)b4r_main::_decrypted->data, b4r_main::_decrypted_len,
                                (uint8_t*)b4r_main::_encrypted->data, &olen,b4r_main::_encrypted->length,
                                mbedtls_ctr_drbg_random, &ctr_drbg ) )

As you can see I can use global variables. Later I use

C:

b4r_main::_encrypted_len = olen;

to modify encrypted_len in globals (Public encrypted_len As Int) which works fine.

Problem: I want to use b4r_main::_encrypted_len directly in the function (like the other values):

C:

mbedtls_pk_encrypt( &pk, (uint8_t*)b4r_main::_decrypted->data, b4r_main::_decrypted_len,
                               (uint8_t*)b4r_main::_encrypted->data, (uint8_t*)b4r_main::_encrypted_len,b4r_main::_encrypted->length,
                                mbedtls_ctr_drbg_random, &ctr_drbg ) )

This throws an error:

b4r_main.cpp:488:68: error: cannot convert 'uint8_t* {aka unsigned char*}' to 'size_t* {aka unsigned int*}' for argument '5' to 'int mbedtls_pk_encrypt(mbedtls_pk_context*, const unsigned char*, size_t, unsigned char*, size_t*, size_t, int (*)(void*, unsigned char*, size_t), void*)'

So how do I cast it correctly?

C:

b4r_main::_encrypted_len = olen;

works, but I want to use it directly in the function.

candide · Jan 22, 2023

did you solve your problem ?

from error, size_t is uint* , it should be better to have variable uint in B4R and cast can be (uint16_t*)

KMatle · Jan 22, 2023

Thanks for your reply. I tried several things (uint/Int), cast to uint_16t* and even unsigned_int* or size_t*. Either it didn't compile (x cannot be casted to y) or it compiled and then I go a kernal panic/crash (memory violation).

So I still use

C:

b4r_main::_encrypted_len = olen;

which works

KMatle · Jan 22, 2023

When I use

C:

Public decrypted_len As UInt

or

Public decrypted_len As Int

with Inline C:

C:

...b4r_main::_encrypted_len, (uint8_t*)b4r_main::_decrypted->data, [B](size_t*)b4r_main::_decrypted_len[/B],...

It compiles but throws

Guru Meditation Error: Core 1 panic'ed (StoreProhibited). Exception was unhandled.

B4R Question size_t* to global variable

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