Anfängerfrage zu strlen

#include "global.h"

#include <avr/io.h>

#include <avr/interrupt.h>

#include <util/delay.h>

#include <string.h>

#include "AVRlib/buffer.h"

#define  buffer_size   32

char UART0_TX_Buffer_String[buffer_size];

cBuffer UART0_TX_Buffer;

char CMD_String[32];

ISR( USART0_UDRE_vect ) 

  {

    UDR0 = bufferGetFromFront (&UART0_TX_Buffer);

    if (UART0_TX_Buffer.datalength = 0)

    {

      UCSR0B &= ~(1<< UDRIE0); // USART0 Data Register Empty Interrupt Disable

    }

  }

void InitUart0 (void)

{

  // UART0

  UBRR0 = (config_UBRR0 & 0x0FFF);    // Baudrateneinstellung nur die niederwertigsten 12Bit

  UCSR0B |= (1<<TXEN0);          // Enable TX Funktion 

}

int main(void)

{  

  uint8_t len = 0;

  // Debug

   DDRB = 0x00;

   DDRB |= (1<<PB0)| (1<<PB1);

   // Init Sendebuffer für UART0

   bufferInit(&UART0_TX_Buffer, UART0_TX_Buffer_String, buffer_size);

  InitUart0();  // UART0

  UCSR0B |= (1<< UDRIE0);          // USART0 Data Register Empty Interrupt Enable

  sei();

  strcpy( CMD_String, "Hallo Welt" );

    while (1) 

    {

    volatile int Laenge = strlen(CMD_String);

    for (len = 0; len < Laenge ; len++);

    {

       bufferAddToEnd  (&UART0_TX_Buffer,CMD_String[len]); 

    }

    UCSR0B |= (1<< UDRIE0); // USART0 Data Register Empty Interrupt Enable

  }

}