c++ float能到小數點后多少位

float xiaoshu=0.0000000000000000000000000000000000000000000001;
cout<<"xiaoshu"<<xiaoshu<<endl;
double xiaoshu1=0.0000000000000000000000000000000000000000000001;
cout<<"xiaoshu1"<<xiaoshu1<<endl;

結果分別為0和11e-046

float xiaoshu=0.000000000000000000000000000000000000000000001;
    cout<<"xiaoshu"<<xiaoshu<<endl;
    double xiaoshu1=0.000000000000000000000000000000000000000000001;
    cout<<"xiaoshu1"<<xiaoshu1<<endl;

結果分別為1.4013e-045和11e-45(前后兩端代碼僅差一個0)