Convert char* to uint8_t

I transfer message trough a CAN protocol.

To do so, the CAN message needs data of uint8_t type. So I need to convert my char* to uint8_t. With my research on this site, I produce this code :

 char* bufferSlidePressure = ui->canDataModifiableTableWidget->item(6,3)->text().toUtf8().data();//My char* /* Conversion */ uint8_t slidePressure [8]; sscanf(bufferSlidePressure,"%c", &slidePressure[0]); 

As you may see, my char* must fit in sliderPressure[0].

My problem is that even if I have no error during compilation, the data in slidePressure are totally incorrect. Indeed, I test it with a char* = 0 and I 've got unknow characters ... So I think the problem must come from conversion.

My datas can be Bool, Uchar, Ushort and float.

Thanks for your help.

4 Answers

Is your string an integer? E.g. char* bufferSlidePressure = "123";?

If so, I would simply do:

uint8_t slidePressure = (uint8_t)atoi(bufferSlidePressure); 

Or, if you need to put it in an array:

slidePressure[0] = (uint8_t)atoi(bufferSlidePressure); 

Edit: Following your comment, if your data could be anything, I guess you would have to copy it into the buffer of the new data type. E.g. something like:

/* in case you'd expect a float*/ float slidePressure; memcpy(&slidePressure, bufferSlidePressure, sizeof(float)); /* in case you'd expect a bool*/ bool isSlidePressure; memcpy(&isSlidePressure, bufferSlidePressure, sizeof(bool)); /*same thing for uint8_t, etc */ /* in case you'd expect char buffer, just a byte to byte copy */ char * slidePressure = new char[ size ]; // or a stack buffer memcpy(slidePressure, (const char*)bufferSlidePressure, size ); // no sizeof, since sizeof(char)=1 

uint8_t is 8 bits of memory, and can store values from 0 to 255

char is probably 8 bits of memory

char * is probably 32 or 64 bits of memory containing the address of a different place in memory in which there is a char

First, make sure you don't try to put the memory address (the char *) into the uint8 - put what it points to in:

char from; char * pfrom = &from; uint8_t to; to = *pfrom; 

Then work out what you are really trying to do ... because this isn't quite making sense. For example, a float is probably 32 or 64 bits of memory. If you think there is a float somewhere in your char * data you have a lot of explaining to do before we can help :/

char * is a pointer, not a single character. It is possible that it points to the character you want.

uint8_t is unsigned but on most systems will be the same size as a char and you can simply cast the value.

You may need to manage the memory and lifetime of what your function returns. This could be done with vector< unsigned char> as the return type of your function rather than char *, especially if toUtf8() has to create the memory for the data.

Your question is totally ambiguous.

ui->canDataModifiableTableWidget->item(6,3)->text().toUtf8().data(); 

That is a lot of cascading calls. We have no idea what any of them do and whether they are yours or not. It looks dangerous.

More safe example in C++ way

char* bufferSlidePressure = "123"; std::string buffer(bufferSlidePressure); std::stringstream stream; stream << str; int n = 0; // convert to int if (!(stream >> n)){ //could not convert } 

Also, if boost is availabe

int n = boost::lexical_cast<int>( str )