如何检查用户输入的数字不大于LLONG_MAX或小于LLONG_MIN? [英] How to check that an user inputted number isn't bigger than LLONG_MAX or LOWER than LLONG_MIN?

问题描述

我要检查用户输入的数字是否大于或小于告知的值.

I want to check if an user inputted number is bigger or lower than the told values.

我了解 atoll函数，但似乎没有为了特别有用，将检查基于未定义的值似乎不太有说服力.

I know about atoll function but it doesn't seem to be specially helpful, basing the check on a undefined value doesn't look too convincing.

我也知道我可以检查用户输入的字符串是否全为数字，在这种情况下，我可以检查一下字符串的长度是否大于LLONG_MAX或LLONG_MIN的长度删除了左侧的0，或者在两者的长度相同的情况下，我可以逐位检查数字，并且如果该数字中输入的数字的值大于LLONG_MAX或LLONG_MIN的值，它会超出范围.

I also know that I could check if the string the user has inputted is all digits, in this case I could check for things as if the length of the string is bigger than the length of LLONG_MAX or LLONG_MIN once 0s on the left are removed, or in the case the length of both is the same I could go checking digit by digit and if the value of the inputted number in that digit is bigger than the value of LLONG_MAX or LLONG_MIN the it would be out of range.

但是我想必须有一个更好的方法来做到这一点.希望您能给我有关哪种方法的提示.

But I guess there has to be a better way to do this. Hope you can give me tips about which that way is.

推荐答案

请改用strtoll函数.

如果输入的值超出范围，则将errno设置为ERANGE，并根据值是下溢还是上溢返回LLONG_MIN或LLONG_MAX.

In case the inputted value is out of range, errno is set to ERANGE and either LLONG_MIN or LLONG_MAX are returned, depending on whether the value underflows or overflows.

在手册页中:

strtol()函数返回转换结果，除非 该值将下溢或上溢.如果发生下溢， strtol()返回LONG_MIN.如果发生溢出，strtol() 返回LONG_MAX.在这两种情况下，errno都设置为ERANGE.恰恰 对于strtoll()也是一样(对于LLONG_MIN和LLONG_MAX 而不是LONG_MIN和LONG_MAX).

The strtol() function returns the result of the conversion, unless the value would underflow or overflow. If an underflow occurs, strtol() returns LONG_MIN. If an overflow occurs, strtol() returns LONG_MAX. In both cases, errno is set to ERANGE. Precisely the same holds for strtoll() (with LLONG_MIN and LLONG_MAX instead of LONG_MIN and LONG_MAX).

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