c++ - What is special about numbers starting with zero?

Question

This is kinda stupid question, but it's interesting for me )

This is what i get with visual studio 2013

int i = 07;     // i == 7
int i = 16;     // i == 16
int i = 00016;  // i == 14, why?
int i = 05016;  // i == 2574, wow )
int i = 08;     // compile error, compiler expects octal number...

If number starts with zero and contains 8, it's compile error. Is this normal? And what exactly compiler does with starting zeros if 00016 == 14?

Thanks to all ))

Answer 1

Yes, this is expected.

[C++11: 2.14.2/1]: An integer literal is a sequence of digits that has no period or exponent part. An integer literal may have a prefix that specifies its base and a suffix that specifies its type. The lexically first digit of the sequence of digits is the most significant. A decimal integer literal (base ten) begins with a digit other than 0 and consists of a sequence of decimal digits. An octal integer literal (base eight) begins with the digit 0 and consists of a sequence of octal digits.²² A hexadecimal integer literal (base sixteen) begins with 0x or 0X and consists of a sequence of hexadecimal digits, which include the decimal digits and the letters a through f and A through F with decimal values ten through fifteen. [ Example: the number twelve can be written 12, 014, or 0XC. —end example ]

^{22 The digits 8 and 9 are not octal digits.}