C Integers 2018 8 1 1 GCC supports

C Integers 袁建鹏 2018. 8. 1 1

GCC supports only two’s complement integer types 0 0 1 0 x [1, 128] ~ 1 1 0 1 255 -x + 1 1 1 0 255 -x+1 signed: -x unsigned: 256 -x 3

Integer Constants decimal-constant 123 Suffix Decimal Constant Octal or Hexadecimal Constant none int long int hexadecimal-constant 0 xffff int unsigned int long int unsigned long int U integer-suffix u U l L ll LL unsigned int unsigned long long int L long int long int unsigned long int UL unsinged long int unsigned long int LL long int unsigned long int ULL unsigned long int octal-constant 0644 A plus (+) or minus (-) symbol can precede an integer literal. The operator is treated as a unary operator rather than as part of the literal. 4

Convertions C 99：Conversion of an operand value to a compatible type causes no change to the value or the representation. Zero extentions 高位填充0 Signed extentions 高位填充符号位 从高精度到底精度整数转换：直接 截断取低部分！！！ 当操作数为两种不同的类型时， 低rank类型的操作数被转换成高 类型的rank long double float unsigned long unsigned long unsigned int 5

Shift Logical Shift Left Logical Shift Right Arithmetic Shift Right 没有算术左移，why？ 注意左边空出的所有位都填充符号位， 而不是只有最高位填充 6

Integer promotions C 99：If an int can represent all values of the original type, the value is converted to an int; otherwise, it is converted to an unsigned int. These are called the integer promotions. 48) All other types are unchanged by the integer promotions. 当char short出现在表达式中，不管有无符号，都被转换成int或者unsigned int Integer Overflow 溢出位被截断 7

思考1 memset(data, -1, len); 8