Why Do Zero-Prepended Numbers Behave Unexpectedly in C ?

Understanding the Peculiar Behavior of Zero-Prepended Numbers

It is often observed that in certain programming languages like C , numerals prefixed with zero exhibit unexpected behavior. Let's delve into the specific scenarios you presented to comprehend these quirks.

Consider the following code excerpts:

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...

Zero Digits and Octal Interpretation

In C , integer literals can be specified in decimal, octal, or hexadecimal bases. Zero-prepended integers are typically interpreted as octal literals, except when the literal begins with 0x or 0X, which indicates a hexadecimal base.

In your example, 00016 is interpreted as an octal literal, resulting in i == 14. Octal numbers represent values using the digits 0-7. The leading zeros do not affect the value of the literal.

Similarly, 05016 is also interpreted as an octal literal, which can be converted to decimal by multiplying each digit by the appropriate power of 8. This gives us i == 2574.

Leading Zeros and Hexadecimal Interpretation

However, if the literal begins with 0x or 0X, it is interpreted as a hexadecimal literal. Hexadecimal numbers represent values using the digits 0-9 and the letters A-F (or a-f).

In your example, 0x16 would be interpreted as a hexadecimal literal representing the value 22.

Octal Digits and Syntax Error

According to the C standard, 8 and 9 are not valid octal digits. Therefore, 08 is an invalid octal literal and results in a syntax error during compilation.

Conclusion

The quirks you observed with zero-prepended numbers stem from the specific rules for interpreting integer literals in C . By understanding these rules (namely, interpreting zero-prepended integers as octal literals unless specified otherwise), you can avoid errors and correctly handle integer values.

The above is the detailed content of Why Do Zero-Prepended Numbers Behave Unexpectedly in C ?. For more information, please follow other related articles on the PHP Chinese website!