I have this piece of code that if compiled as debug works properly, if compiled in release processes the first sequence then exits.

Here is a dump of the data fed to the code:

00 19 01 00 - 00 63 01 00 - 00 67 01 00 - 00 68 01 00

//this is a variable length sequence 00 19 01 00
//0x0019 -> first value (WORD)
//0x01   -> 1B payload  (BYTE)
//0x00   -> Value of 00 (BYTEs)

size_t parse(BYTE* DATA, size_t out_size){
BYTE t[258]; // my buffer

 size_t b, //byte counter
        i; //sequence counter
       
 for (b=0 ,i = 0; i<33&& b<out_size; i++ ){
        
        memset(&t, 0, sizeof(t));
    
        int err=-1;
        
        err = memcpy_s( &(t.m_type),sizeof(t)-b, DATA + b,sizeof(t.m_type)); b += sizeof(t.m_type); //2
        if (err) { printf("!!Memcpy_s failed!!n"); return 0; }
    
        err = memcpy_s( &(t.m_len), sizeof(t)-b, DATA+b,sizeof(t.m_len)); b += sizeof(t.m_len); //1
        if (err) { printf("!!Memcpy_s failed!!n"); return 0; }
        

        //this second way works also in release
        //err = memcpy_s(&t, sizeof(t)-b, DATA + b, 3); b += 2; b += 1; // single step copy
        //if (err) { printf("!!Memcpy_s failed!!n"); return 0; }

   // this piece of code execute in both cases
        err = memcpy_s( &(t.m_value), sizeof(t)-b, DATA + b, t.m_len);  b += t.m_len;
        if (err) { printf("!!Memcpy_s failed!!n"); return 0; }

        //memcpy(&out[ i ], &t, sizeof(t));
    
        
        out[ i ] = t;
        

        if (t.isEmpty()) {
// as soon as I get a data structure that is empty I exit
            printf("Breaking empty data found i:%d,  (b:%d)n", i,  b);
            break; 
        } 
        
    }

    return i; 
}

in debug I get in the output a structure containing all 3 the elements correctly parsed
in release I got only the first sequence (into the out variable)

Why?

I’m On visual studio 2022, compiling as x86