memset对于int、long long、float、double 的极值怎么清

出处[辗转山河弋流歌 by 空灰冰魂]
原网址：blog.csdn.net/vmurder/article/details/46537613

int
”较“的原则：加法不爆。
极大值：0x7f
较大值：0x3f
较小值：0xc0
极小值：0x80

long long
”较“的原则：加法不爆。
极大值：0x7f
较大值：0x3f
较小值：0xc0
极小值：0x80

float
”较“的原则：保证一定位精度。
7f以上一直到be都是-0 (实际上是一个很小的>-1.0的负数)
极大值：0x7f
较大值：0x4f
较小值：0xce
极小值：0xfe
0xff是 -1.#QNAN0000…… (-∞？)

double
”较“的原则：保证一定位精度。
极大值：0x7f
较大值：0x43
较小值：0xc2
极小值：0xfe

实验代码：

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#define N 5using namespace std;int a[N];long long b[N];float c[N];double d[N];void _int(){    puts("");    puts("int:");    puts("");    memset(a,0x7f,sizeof a);printf("%d\n",a[0]);    memset(a,0x80,sizeof a);printf("%d\n",a[0]);    memset(a,0x81,sizeof a);printf("%d\n",a[0]);    puts("");    memset(a,0xbf,sizeof a);printf("%d %d\n",a[0],a[0]*2);    memset(a,0xc0,sizeof a);printf("%d %d\n",a[0],a[0]*2);    memset(a,0xc1,sizeof a);printf("%d %d\n",a[0],a[0]*2);    puts("");    memset(a,0x3e,sizeof a);printf("%d %d\n",a[0],a[0]*2);    memset(a,0x3f,sizeof a);printf("%d %d\n",a[0],a[0]*2);    memset(a,0x40,sizeof a);printf("%d %d\n",a[0],a[0]*2);    puts("");    memset(a,0x7e,sizeof a);printf("%d\n",a[0]);    memset(a,0x7f,sizeof a);printf("%d\n",a[0]);    memset(a,0x80,sizeof a);printf("%d\n",a[0]);}void _long(){    puts("");    puts("long long:");    puts("");    memset(b,0x7f,sizeof b);printf("%I64d\n",b[0]);    memset(b,0x80,sizeof b);printf("%I64d\n",b[0]);    memset(b,0x81,sizeof b);printf("%I64d\n",b[0]);    puts("");    memset(b,0xbf,sizeof b);printf("%I64d %I64d\n",b[0],b[0]*2);    memset(b,0xc0,sizeof b);printf("%I64d %I64d\n",b[0],b[0]*2);    memset(b,0xc1,sizeof b);printf("%I64d %I64d\n",b[0],b[0]*2);    puts("");    memset(b,0x3e,sizeof b);printf("%I64d %I64d\n",b[0],b[0]*2);    memset(b,0x3f,sizeof b);printf("%I64d %I64d\n",b[0],b[0]*2);    memset(b,0x40,sizeof b);printf("%I64d %I64d\n",b[0],b[0]*2);    puts("");    memset(b,0x7e,sizeof b);printf("%I64d\n",b[0]);    memset(b,0x7f,sizeof b);printf("%I64d\n",b[0]);    memset(b,0x80,sizeof b);printf("%I64d\n",b[0]);}void _float(){    puts("");    puts("float:");    puts("");    memset(c,0xfd,sizeof c);printf("%f\n",c[0]);    memset(c,0xfe,sizeof c);printf("%f\n",c[0]);    memset(c,0xff,sizeof c);printf("%f\n",c[0]);    puts("");    memset(c,0xcd,sizeof c);printf("%f %f\n",c[0],c[0]*2);    memset(c,0xce,sizeof c);printf("%f %f\n",c[0],c[0]*2);    memset(c,0xcf,sizeof c);printf("%f %f\n",c[0],c[0]*2);    puts("");    memset(c,0x4e,sizeof c);printf("%f %f\n",c[0],c[0]*2);    memset(c,0x4f,sizeof c);printf("%f %f\n",c[0],c[0]*2);    memset(c,0x50,sizeof c);printf("%f %f\n",c[0],c[0]*2);    puts("");    memset(c,0x7e,sizeof c);printf("%.15f\n",c[0]);    memset(c,0x7f,sizeof c);printf("%.15f\n",c[0]);    memset(c,0x80,sizeof c);printf("%.15f\n",c[0]);}void _double(){    puts("");    puts("double:");    puts("");    memset(d,0xfd,sizeof d);printf("%lf\n",d[0]);    memset(d,0xfe,sizeof d);printf("%lf\n",d[0]);    memset(d,0xff,sizeof d);printf("%lf\n",d[0]);    puts("");    memset(d,0xc1,sizeof d);printf("%lf %lf\n",d[0],d[0]*2);    memset(d,0xc2,sizeof d);printf("%lf %lf\n",d[0],d[0]*2);    memset(d,0xc3,sizeof d);printf("%lf %lf\n",d[0],d[0]*2);    puts("");    memset(d,0x42,sizeof d);printf("%lf %lf\n",d[0],d[0]*2);    memset(d,0x43,sizeof d);printf("%lf %lf\n",d[0],d[0]*2);    memset(d,0x44,sizeof d);printf("%lf %lf\n",d[0],d[0]*2);    puts("");    memset(d,0x7e,sizeof d);printf("%lf\n",d[0]);    memset(d,0x7f,sizeof d);printf("%lf\n",d[0]);    memset(d,0x80,sizeof d);printf("%lf\n",d[0]);}int main(){    _int();    _long();    _float();    _double();}