所有例子都在64为操作系统
Linux 2.6.30 x86_64 x86_64 x86_64 GNU/Linux
1.1整数
在stdint.h中定义一些看上去更明确的整数类型
#ifndef __int8_t_defined # define __int8_t_defined typedef signed char int8_t; typedef short int int16_t; typedef int int32_t; # if __WORDSIZE == 64 typedef long int int64_t; # else __extension__ typedef long long int int64_t; # endif #endif /* Unsigned. */ typedef unsigned char uint8_t; typedef unsigned short int uint16_t; #ifndef __uint32_t_defined typedef unsigned int uint32_t; # define __uint32_t_defined #endif #if __WORDSIZE == 64 typedef unsigned long int uint64_t; #else __extension__ typedef unsigned long long int uint64_t; #endif
还有各种整数类型的大小限制：
/* Minimum of signed integral types. */ # define INT8_MIN (-128) # define INT16_MIN (-32767-1) # define INT32_MIN (-2147483647-1) # define INT64_MIN (-__INT64_C(9223372036854775807)-1) /* Maximum of signed integral types. */ # define INT8_MAX (127) # define INT16_MAX (32767) # define INT32_MAX (2147483647) # define INT64_MAX (__INT64_C(9223372036854775807))
字符常量默认是一个int整数，但编译器可以自行决定将其解释为char或者int
char c = 'a'; printf("%c,size(char)=%d,size('a')=%d; ",c,sizeof(c),sizeof('a'));
输出结果为：
a,size(char)=1,size('a')=4;
可以看出sizeof(c)和sizeof('a')的大小不同，后者为int类型，前者为char
指针是个有特殊用途的整数，在stdint.h中同样给出其类型定义：
/* Types for `void *' pointers. */ #if __WORDSIZE == 64 # ifndef __intptr_t_defined typedef long int intptr_t; # define __intptr_t_defined # endif typedef unsigned long int uintptr_t; #else # ifndef __intptr_t_defined typedef int intptr_t; # define __intptr_t_defined # endif typedef unsigned int uintptr_t; #endif
在64位系统中：
printf("%d ",sizeof(int)); printf("%d ",sizeof(long));
输出结果为：
4
8
stdint.h中定义了一些辅助宏：
# define INT8_C(c) c # define INT16_C(c) c # define INT32_C(c) c # if __WORDSIZE == 64 # define INT64_C(c) c ## L # else # define INT64_C(c) c ## LL # endif
对于宏定义中"##"表示什么意思呢？
http://blog.csdn.net/dotphoenix/article/details/4345174
表示把左和右结合在一起，作为一个符号，如下举个例子：
[root@typhoeus79 20131105]# more test.c #include <stdio.h> #include <stdint.h> # define TEST(c) c ## UL int main() { printf("%d ",sizeof(20)); printf("%d ",sizeof(TEST(20))); //20默认是属于int类似，使用TEST宏之后将其转换为UL，无符号长整型 return 0; } [root@typhoeus79 20131105]# ./test 4 8
1.2浮点数
c提供不同精度的浮点：
*float:32位4字节浮点数，精确度为6
*double：64位8字节浮点数，精确度为15
*long double：80位10字节浮点数，精确度为19位
测试结果：
printf("%d ",sizeof(long double)); printf("%d ",sizeof(double)); printf("%d ",sizeof(float));
输出：
16
8
4
对于long double为啥不是10个字节呢？？
对应的文件为bits/mathdef.h
# if __WORDSIZE == 64 || (defined __FLT_EVAL_METHOD__ && __FLT_EVAL_METHOD__ == 0) /* The x86-64 architecture computes values with the precission of the used type. Similarly for -m32 -mfpmath=sse. */ typedef float float_t; /* `float' expressions are evaluated as `float'. */ typedef double double_t; /* `double' expressions are evaluated as `double'. */ # else /* The ix87 FPUs evaluate all values in the 80 bit floating-point format which is also available for the user as `long double'. Therefore we define: */ typedef long double float_t; /* `float' expressions are evaluated as `long double'. */ typedef long double double_t; /* `double' expressions are evaluated as `long double'. */ # endif
c99支持复数，在complex.h中有定义
double complex comp = 1.0 +3.0 * I; printf("%f ",creal(comp)); printf("%f ",cimag(comp));
输出：
1.000000
3.000000
1.3枚举
例子
enum color {black,red=5,green}; enum color b = black; enum color r = red; enum color g = green; printf("black=%d ",b); printf("red=%d ",r); printf("green=%d ",g);
输出结果为：
black=0 red=5 green=6
默认是递增，从0开始，若中间有重新设置，如例子中red=5，后面的还是继续加1
枚举成员的值是可以相同的，这样有什么用呢？？
enum color {black,red=5,green=5}; enum color b = black; enum color r = red; enum color g = green; printf("black=%d ",b); printf("red=%d ",r); printf("green=%d ",g);
输出为：
black=0 red=5 green=5
通常省略枚举小标签用来代替宏定义常量
[root@typhoeus79 20131105]# more test_enum.c #include <stdio.h> int main() { enum {BLACK=0,RED=5,GREEN,YELLOW=5}; printf("%d ",BLACK); printf("%d ",RED); printf("%d ",GREEN); printf("%d ",YELLOW); }
输出：
[root@typhoeus79 20131105]# ./test_enum 0 5 6 5
可以作为定义一些常量使用。