Octal 10-hexadecimal 16 in CPP

1. Neither c nor C ++ provides the expression of binary numbers.

2. How do I express an octal number in C and C ++??

If the number is 876, we can conclude that it is not an octal number, because the octal number cannot contain more than 7 Arabic numbers. However, if the number is 123, 567, or 12345670, it is possible to set the number to octal or decimal.

So, C, C ++ specifies that if a number is specified to use octal, a value of 0 must be added before it.For example, 123 is in decimal format, but 0123 indicates octal.

Int 0123;

This is the expression of Octal numbers in C and C ++. But one exception is the escape letter '\'.

Because C and C ++ do not allow the use of a slash plus a 10-digit number to represent characters, so:

'? '// The ASCII value is 63
'\ 077' // is an octal representation '? ', 0 can be omitted, because C, C ++ does not allow the use of a slash plus a 10-digit number to represent characters
'\ 0x3f' // hexadecimal representation '? '

3. C, C ++ requires that the hexadecimal number must start with 0x.

Int 0x15a

X is not case sensitive. (Note: 0 in 0x is the number 0, not the letter O ).

Note:

1) The octal and hexadecimal values can only be unsigned positive integers. If you are in the Code:-078, or write:-0xf2, C, c ++ does not regard it as a negative number.

2) In QT, convert the decimal integer value to a hexadecimal string.

   int a = 63;     QString s = QString::number(a, 16);                   // s == "3f"     QString t = QString::number(a, 16).toUpper();     // t == "3F"

3) qstring stores hexadecimal values

// Output the string in hexadecimal format: qstring cmd = 0x0a; qdebug () <"cmd:" <cmd. toascii (). tohex ();

4) convert qstring to hexadecimal according to string surface format

QString str = "FF";  bool ok;  int hex = str.toInt(&ok, 16);       // hex == 255, ok == true 0xFF  int dec = str.toInt(&ok, 10);       // dec == 0, ok == false  

4) qbytearray stores hexadecimal values

Static const char mydata [] = {0x00, 0x00, 0x03, 0x84, 0x78, 0x9c, 0x3b, 0x76, 0xec, 0x18, 0xc3, 0x31, 0x0a, 0xf1, 0xcc, 0x99, 0x6d, 0x5b}; qbytearray BD = qbytearray: fromrawdata (mydata, sizeof (mydata); qdebug () <"BD. data: "<BD. data (); qdebug () <"BD. tohex (): "<BD. tohex (); // output hexadecimal value

5) qchar stores hexadecimal values and prints

Qchar c = 0x0a; qbytearray array; array. append (c); qdebug () <array. tohex (); // The result is "0a"

6) char * stores hexadecimal and prints

Char C [] = {0x0a, 0x0b, '\ 0'}; qbytearray array (c); qdebug () <array. tohex (); // result "0a0b"