C 常量的类型

http://bbs.csdn.net/topics/380028485

整型常量的类型是下列相应表中第一个能表示其值的类型：

int --> long int --> long long int

无后缀的十进制整数常量：int，long int，long long int以字母u或U为后缀的十进制整型常量：unsigned int，unsigned long int，unsigned long long int以字母l或L为后缀的十进制整型常量：long int，long long int同时以字母u或U和字母l或L为后缀的十进制整型常量：unsigned long int，unsigned long long int以字母ll或LL为后缀的十进制整型常量：long long int同时以字母u或U和字母ll或LL为后缀的十进制整型常量：unsigned long long int无后缀的八进制或十六进制常量：int，unsigned int，long int，unsigned long int，long long int，unsigned long long int以字母u或U为后缀的八进制或十六进制常量：unsigned int，unsigned long int，unsigned long long int以字母l或L为后缀的八进制或十六进制常量：long int，unsigned long int，long long int，unsigned long long int同时以字母u或U和字母l或L为后缀的八进制或十六进制常量：unsigned long int，unsigned long long int以字母ll或LL为后缀的八进制或十六进制常量：long long int，unsigned long long int同时以字母u或U和字母ll或LL为后缀的八进制或十六进制常量：unsigned long long int

http://www.rapidtables.com/prog/cref/const.htm 

Numbers characters and string constants.

See enum end const in data types page.

Data Type Constants

SyntaxDescriptionExample

0xhexnum

0Xhexnum

hexadecimal numberint x=0x7FFF0000;

0 octnum

octal numberint x=07654321;

num u

num U

unsigned integer number constantunsigned int x=1000U;

num l

num L

long integer number constantlong x=-99999L;

num ul

num UL

unsigned long integer number constantunsigned long x=99999L;

num ll

num LL

long long  integer number constantlong long x=-888888LL;

num ull

num ULL

unsigned long long integer number constantunsigned long long x=100ULL;

num f

num F

float number constantfloat x=0.005F;

num l

num L

long double number constantlong double x=0.005L;

num e±exp

num E±exp

floating point exponent number constantdouble x=5.2E-3;

'char'

character constantchar c='A';

"string"

string constantchar name[6]="Hello";

http://stackoverflow.com/questions/7036056/what-do-0ll-or-0x0ul-mean

These are constants in C and C++. The suffix LL means the constant is of type long long, and UL means unsigned long.

In general, each L or l represents a long and each U or u represents anunsigned. So, e.g.

1uLL // means the constant 1 with type unsigned long long.

 

This also applies to floating point numbers:

1.0f // of type 'float' 1.0 // of type 'double' 1.0L // of type 'long double'

 

and strings and characters, but they are prefixes:

'A' // of type 'char' L'A' // of type 'wchar_t' u'A' // of type 'char16_t' (C++0x only) U'A' // of type 'char32_t' (C++0x only)

In C and C++ the integer constants are evaluated using their original type, which can cause bugs due to integer overflow:

long long nanosec_wrong = 1000000000 * 600; // ^ you'll get '-1295421440' since the constants are of type 'int' // which is usually only 32-bit long, not big enough to hold the result. long long nanosec_correct = 1000000000LL * 600 // ^ you'll correctly get '600000000000' with this int secs = 600; long long nanosec_2 = 1000000000LL * secs; // ^ use the '1000000000LL' to ensure the multiplication is done as 'long long's.

In Google Go, all integers are evaluated as big integers (no truncation happens),

var nanosec_correct int64 = 1000000000 * 600

and there is no "usual arithmetic promotion"

var b int32 = 600 var a int64 = 1000000000 * b // ^ cannot use 1000000000 * b (type int32) as type int64 in assignment

so the suffixes are not necessary.

 

转载于:https://www.cnblogs.com/shangdawei/p/3150554.html