C++ printf string如何处理浮点数

?C++?,????printf?????????????????????????????:

1. ??%f????????,??:

double num = 3.14159;
printf("The value of num is %f\n", num);

2. ??????????,???%f???.???????,??:

double num = 3.14159;
printf("The value of num is %.2f\n", num); // ?????3.14

3. ??%e?%E??????????????,??:

double num = 123456.789;
printf("The value of num is %e\n", num); // ?????1.234568e+05

4. ??????????????,???%f??????,??:

double num = 3.14159;
printf("The value of num is .2f\n", num); // ?????      3.14(????10,??????2)

??????,?????????????,????????