Returns a string with the representation of val.
The format used is the same that printf would print for the corresponding type:
| type of val | printf equivalent | description |
|---|---|---|
| int | "%d" | Decimal-base representation of val. The representations of negative values are preceded with a minus sign (-). |
| long | "%ld | |
| long long | "%lld | |
| unsigned | "%u" | Decimal-base representation of val. |
| unsigned long | "%lu | |
| unsigned long long | "%llu | |
| float | "%f" | As many digits are written as needed to represent the integral part, followed by the decimal-point character and six decimal digits. inf (or infinity) is used to represent infinity. nan (followed by an optional sequence of characters) to represent NaNs (Not-a-Number). The representations of negative values are preceded with a minus sign (-). |
原文：https://www.cnblogs.com/unicornsir/p/14343223.html