Hi want to convert my nsstring to unsigned char I have tried with fallowing line of code
unsigned char strTransforms[100] = (unsigned char) [newTransFarString UTF8String];
but its show a error "Array initializer must be an initializer list"
how can I cast it to unsigned char;
thanks
Have you tried the NSString method – getCString:maxLength:encoding: ?
Related
I'm trying to send a user input String type over Bluetooth with function
BluetoothSerial SerialBT;
SerialBT.write()
But the function won't accept String, but instead it accepts uint8_t.
I tried some conversions like
char buf[packet.length()];
memcpy(buf, packet.c_str(), packet.length());
SerialBT.write(buf, packet.length());
But it shows an error
invalid conversion from 'char*' to 'const uint8_t* {aka const unsigned char*}' [-fpermissive]
Could please someone show me how to convert it right?
Thanks
I am trying to convert a QString to a qint16 with
udpListenPort = ui->lineEdit_UdpListenPort->text().toShort();
but it converts "40690" to 0.
I tried different casts and conversions but neither works. I think I can't see the wood for the trees here.
The maximal value a qint16 (which is a typedef short qint16; /* 16 bit signed */) can hold is 32767 using two's complement, hence "40690" overflows and signed integer overflow is undefined behaviour.
Use quint16 instead (which is a typedef unsigned short quint16; /* 16 bit unsigned */) and ushort QString::toUShort(bool *ok = nullptr, int base = 10) const.
You came most of the way, just change the toShort() to toUShort() to fix that.
udpListenPort = ui->lineEdit_UdpListenPort->text().toUShort();
quint16 is just a typedef for unsigned short.
I'm not able to understand the output of this simple c code.What happens when we typecast a int value to char pointer?
int main(void) {
int a =320;
char *ptr;
ptr=(char *)&a;
printf("%d",*ptr);
return 0;
}
the output is 64.But I'm unable to figure out the logic.Does the size of the signed char play a role here?
320 is 0x140 in hex. A char is one byte (Two hexadecimal digits), so casting and printing with %d will print the decimal value of 0x40, which happens to be 64.
I have a pointer to some location in memory passed in, void *dataLoc.
Some program is transferring memory there as a bunch of unsigned chars where 0x00 is 0 and 0xFF is one.
I want to be able to pull, say, every 4th char and convert it to the float of what number is supposed to be represented. But I'm having trouble understanding how I get from a void * to an array of char[] to an array of float[].
My initial thought was to do something like
for(i=0,i<100,i++){
floatArray[i] = (float)(*((unsigned char *)dataLoc[4*i])) / 255;
}
the void * is cast to a char *.
the next 4th char is selected from the for loop
the * dereferences the char pointer, which should give me an unsigned char,
the float should change the char into a float, but a float representation of the number I want *255
I divide by 255 to get the fraction I want.
This fails, because I get the error "pointer of type 'void ' used in arithmetic
'void' is not a pointer-to-object type and beyond this, I'm not really confident that the rest of that line will work out the way I would like.
Can someone advise the proper way to handle this?
Good that you had warnings enabled.
dataLoc[4*i] occurs before (unsigned char *)dataLoc and leads to "pointer of type 'void *' used in arithmetic ..."
Cast to unsigned char * first.
Also remove extra level of *. The following is type unsigned char
((unsigned char *)dataLoc)[4*i]
Fixed:
void * dataLoc;
float floatArray[100];
// for(i=0,i<100,i++){ Use ';', not ','
for(int i=0;i<100;i++){
// Cast to `unsigned char *` before using `[]`
// * not needed here ---v
floatArray[i] = (float)( ( ((unsigned char *)dataLoc) [4*i])) / 255;
}
or
for (int i=0; i<100 ;i++) {
unsigned char value = ((unsigned char *)dataLoc)[4*i];
floatArray[i] = value / 255.0f;
}
I'm trying to convert raw hex/binary data to different file types.
#include <QByteArray>
#include <QDebug>
int main(int argc, char *argv[])
{
QByteArray package;
package.append( QByteArray::fromHex("a1"));
// "a1" is what is written to the memory, not the string representation of "a1"
qDebug() << package.toHex(); // "a1"
qDebug() << package; // "�"
qDebug() << package.toInt(); // 0
}
Why is the int representation 0 and not 161?
toInt has totally different purpose. It parses string representation of integer. If you want integer representing the value of the first byte of the array, use package[0]. It has char type. I don't remember how qDebug() represents char type, but if you have any problems with it, just static_cast it to unsigned int.
QByteArray::toInt expects that QByteArray contains a string of characters (in ASCII probably), not the binary representation of the number.
If you want to convert binary representation to integer you can use reinterpret_cast:
int i = *reinterpret_cast<quint8*>(package.constData());
Or better use qFromBigEndian/qFromLittleEndian:
int i = qFromLittleEndian<quint8>((const uchar*)package.constData())
In both cases you must know exactly in what format the number is stored and use proper type and endianness.