4 byte uint8_t array to integer conversion.

GunkutA

Hello, I am trying to make a TCP connection with some client. Client keep sending me an integer value in an uint8_t array. Since it is an integer value it is 4 bytes. I am trying to use this values (printing, putting into table etc.) However, when I try to convert this 4 byte uint8_t array into integer. That becomes a completely different data.
I try this line in order to convert that array into integer and then to string:

convertedString= QString::number(*(int*)receivedFrame.data);

receivedFrame is a structure:

typedef struct{

    //! Variable which holds the header data of the  Frame
    HEADER headerData;

    //! Data contained in the variable size portion of the
    uint8_t data[MAX_DATA_LENGTH];
}FRAME;

How can convert this uint8_t data array into an integer? Thanks beforehand.

J.Hilk

@GunkutA
you can also try something like this,

uint32_t i32 = receivedFrame.data[0] | (receivedFrame.data[1] << 8) | (receivedFrame.data[2] << 16) | (receivedFrame.data[3] << 24);

Simply change around the indices for a correction of the byte order

Christian Ehrlicher

@GunkutA said in 4 byte uint8_t array to integer conversion.:

convertedString= QString::number((int)receivedFrame.data);

an ampersand is missing, using c++ functionality would have given a compiler error

int value = reinterpret_cast<int>(&receivedFrame.data);

J.Hilk

@GunkutA
you can also try something like this,

uint32_t i32 = receivedFrame.data[0] | (receivedFrame.data[1] << 8) | (receivedFrame.data[2] << 16) | (receivedFrame.data[3] << 24);

Simply change around the indices for a correction of the byte order

GunkutA

@Christian-Ehrlicher That gives me "cast from pointer to smaller type 'int' loses information" error. I think I forgot to add the complete function which is:

QString protocolForm::convertToString(uint8_t *data,int dataLength)
{
    FRAME receivedFrame;
    memcpy(&receivedFrame,data,dataLength);
memcpy(&receivedHeader, receivedFrame.data, sizeof(PARAM_DATA_HEADER));
convertedString= QString::number(*(int*)&receivedFrame.data);
}

So data is a pointer

Christian Ehrlicher

This is not an error, just a warning which is understandable since you do some crude casting (but in this case it's wanted)

GunkutA

Sorry I tried to use it in switch statement. Then it gave

jump tp case label [-fpermissive] 
note: crosses initialization of'int integer'

Error with

cast from 'uint8_t (*) [255] {aka unsigned char (*) [255]} 'to 'int' loses precision [-fpermissive]

error.

GunkutA

@GunkutA said in 4 byte uint8_t array to integer conversion.:

jump tp case label [-fpermissive]
note: crosses initialization of

When I added { } to the case I got rid of the first error. But

cast from 'uint8_t (*) [255] {aka unsigned char (*) [255]} 'to 'int' loses precision [-fpermissive]

error still remains.

Christian Ehrlicher

@GunkutA said in 4 byte uint8_t array to integer conversion.:

error still remains.

~~This is no error, it's a warning that the cast is not really a good idea and int should be used in the first place in your struct.~~ You can get rid of it by using @J-Hilk 's suggestion

The forum displays it wrong:

int value = *reinterpret_cast<int *>(&receivedFrame.data);

Now it's fine, must be a space between 'int' and '' - otherwise the forum eats the '' - sorry.