izeof(float)（314是float还是double）

瑞英

对于c语言来说，数据类型是一个很重要的概念和知识点，它涉及到的是内存的空间，这在和硬件交互的时候是非常重要的。 K&R给出了7个数据类型相关的关键字，分别是：int、long、short、unsigned、char、float、double。后来C90增加了2个关键字，分别是：signed、void。再后来，C99又增加了3个关键字，分别是：_Bool、_Complex、_Imaginary。 整体来说，我们可以分为2个系列：分别是整数类型和浮点数类型。 下面就依次来说说了（环境：win7 64bit 、VS2015）： int（有符号整型）占用的字节数：printf("int:bytes %d;bit %dn", sizeof(int), sizeof(int) * 8);int:bytes 4;bit 32取值范围：printf("int:MIN %d;MAX %dn", INT_MIN, INT_MAX);int:MIN -2147483648;MAX 2147483647 即-2^31~2^31-1格式说明符：%d（十进制）、%o（八进制）、%x（十六进制）unsigned int（无符号整型）占用的字节数：printf("unsigned int:bytes %d;bit %dn", sizeof(unsigned int), sizeof(unsigned int) * 8);unsigned int:bytes 4;bit 32取值范围：printf("unsigned int:MIN is 0;MAX %un", UINT_MAX);unsigned int:MIN is 0;MAX 4294967295 即0~2^32格式说明符：%u（十进制）char（有符号字符型）占用的字节数：printf("char:bytes %d;bit %dn", sizeof(char), sizeof(char) * 8);char:bytes 1;bit 8取值范围：printf("char:MIN %d;MAX %dn", CHAR_MIN, CHAR_MAX);char:MIN -128;MAX 127 即-2^7~2^7-1格式说明符：%d（十进制）unsigned char(无符号字符型)占用的字节数：printf("unsigned char:bytes %d;bit %dn", sizeof(unsigned char), sizeof(unsigned char) * 8);unsigned char:bytes 1;bit 8取值范围：printf("unsigned char:MIN is 0;MAX %dn", UCHAR_MAX);unsigned char:MIN is 0;MAX 255 即0~2^8-1格式说明符：%d（十进制）short（有符号短整型）占用的字节数：printf("short:bytes %d;bit %dn", sizeof(short), sizeof(short) * 8);short) 2;bit 16取值范围：printf("short :MIN %hd;MAX %hdn", SHRT_MIN, SHRT_MAX);short :MIN -32768;MAX 32767 即-2^15~2^15-1格式说明符：%hd（十进制）unsigned short（无符号短整型）占用的字节数：printf("unsigned short:bytes %d;bit %dn", sizeof(unsigned short), sizeof(unsigned short) * 8);unsigned short:bytes 2;bit 16:bytes 2;bit 16取值范围：printf("unsigned short:MIN is 0;MAX %dn", USHRT_MAX);unsigned short:MIN is 0;MAX 65535 即0~2^16-1格式说明符：%hd（十进制）long（有符号长整型）占用的字节数:printf("long:bytes %d;bit %dn", sizeof(long), sizeof(long) * 8);long:bytes 4;bit 32取值范围：printf("long :MIN %ld;MAX %ldn", LONG_MIN, LONG_MAX);long :MIN -2147483648;MAX 2147483647 即-2^31~2^31-1格式说明符：%ldunsigned long(无符号长整型)占用的字节数:unsigned long:bytes %d;bit %dn", sizeof(unsigned long), sizeof(unsigned long) * 8);unsigned long:bytes 4;bit 32取值范围：printf("unsigned long:MIN is 0;MAX %lun", ULONG_MAX);unsigned long:MIN is 0;MAX 4294967295 即0~2^32-1格式说明符：%lulong long（有符号长长整型）占用的字节数:printf("long long :bytes %d;bit %dn", sizeof(long long), sizeof(long long) * 8);long long :bytes 8;bit 64取值范围：printf("long long :MIN %lld;MAX %llun", LLONG_MIN, LLONG_MAX);long long :MIN -9223372036854775808;MAX 9223372036854775807 即-2^63~2^63-1格式说明符：%lluunsigned long long(有符号的长长整型)占用的字节数:printf("unsigned long long:bytes %d;bit %dn", sizeof(unsigned long long), sizeof(unsigned long long) * 8);unsigned long long:bytes 8;bit 64取值范围：printf("unsigned long long:MIN is 0;MAX %llun", ULLONG_MAX);unsigned long long:MIN is 0;MAX 18446744073709551615 即0~2^64-1格式说明符：%llufloat （单精度浮点型）占用的字节数：printf("float :bytes %d;bit %dn", sizeof(float), sizeof(float) * 8);float :bytes 4;bit 32取值范围：C标准规定，float类型至少能表示6位有效数字，范围至少为10^-37~10^37诸如：22.333444这样的数。其中8bit用于表示指数及其符号，24bit表示尾数或有效数字及其符号。 double（双精度浮点型）占用的字节数：printf("float :bytes %d;bit %dn", sizeof(float), sizeof(float) * 8);double :bytes 8;bit 64取值范围：C标准规定，double类型至少能表示10位有效数字。一些系统将多出来的32bit都来表示尾数部分，这就至少有13位有效数字了，这也超出了c规定的最小标准了。longdouble占用的字节数：printf("long double :bytes %d;bit %dn", sizeof(long double), sizeof(long double) * 8);long double :bytes 8;bit 64 取值范围：理论上是比double有更高的精度，但是c只保证long double至少同double 一样的精度 源码：include include int main() { printf("int:bytes %d;bit %dn", sizeof(int), sizeof(int) * 8); //int:bytes 4;bit 32 printf("int:MIN %d;MAX %dn", INT_MIN, INT_MAX); // int:MIN -2147483648;MAX 2147483647 printf("unsigned int:bytes %d;bit %dn", sizeof(unsigned int), sizeof(unsigned int) * 8); //unsigned int:bytes 4;bit 32 printf("unsigned int:MIN is 0;MAX %un", UINT_MAX); //unsigned int:MIN is 0;MAX 4294967295 printf("-------------------------------------------------------n"); printf("char:bytes %d;bit %dn", sizeof(char), sizeof(char) * 8); // char:bytes 1;bit 8 printf("char:MIN %d;MAX %dn", CHAR_MIN, CHAR_MAX); // char:MIN -128;MAX 127 printf("unsigned char:bytes %d;bit %dn", sizeof(unsigned char), sizeof(unsigned char) * 8); //unsigned char:bytes 1;bit 8 printf("unsigned char:MIN is 0;MAX %dn", UCHAR_MAX); // unsigned char:MIN is 0;MAX 255 printf("-------------------------------------------------------n"); printf("short:bytes %d;bit %dn", sizeof(short), sizeof(short) * 8); // short:bytes 2;bit 16 printf("short :MIN %hd;MAX %hdn", SHRT_MIN, SHRT_MAX); // short :MIN -32768;MAX 32767 printf("unsigned short:bytes %d;bit %dn", sizeof(unsigned short), sizeof(unsigned short) * 8); //unsigned short:bytes 2;bit 16 printf("unsigned short:MIN is 0;MAX %dn", USHRT_MAX); // unsigned short:MIN is 0;MAX 65535 printf("-------------------------------------------------------n"); printf("long:bytes %d;bit %dn", sizeof(long), sizeof(long) * 8); // long:bytes 4;bit 32 printf("long :MIN %ld;MAX %ldn", LONG_MIN, LONG_MAX); // long :MIN -2147483648;MAX 2147483647 printf("unsigned long:bytes %d;bit %dn", sizeof(unsigned long), sizeof(unsigned long) * 8); //unsigned long:bytes 4;bit 32 printf("unsigned long:MIN is 0;MAX %lun", ULONG_MAX); // unsigned long:MIN is 0;MAX 4294967295 printf("-------------------------------------------------------n"); printf("long long :bytes %d;bit %dn", sizeof(long long), sizeof(long long) * 8); // long long :bytes 8;bit 64 printf("long long :MIN %lld;MAX %llun", LLONG_MIN, LLONG_MAX); // long long :MIN -9223372036854775808;MAX 9223372036854775807 printf("unsigned long long:bytes %d;bit %dn", sizeof(unsigned long long), sizeof(unsigned long long) * 8); //unsigned long long:bytes 8;bit 64 printf("unsigned long long:MIN is 0;MAX %llun", ULLONG_MAX); // unsigned long long:MIN is 0;MAX 18446744073709551615 printf("-------------------------------------------------------n"); printf("float :bytes %d;bit %dn", sizeof(float), sizeof(float) * 8); // float :bytes 4;bit 32 printf("double :bytes %d;bit %dn", sizeof(double), sizeof(double) * 8); // double :bytes 8;bit 64 printf("long double :bytes %d;bit %dn", sizeof(long double), sizeof(long double) * 8); // long double :bytes 8;bit 64 printf("-------------------------------------------------------n"); return 0;