为time_t的最大值（结构的timespec） [英] Maximum values for time_t (struct timespec)

问题描述

我使用的是结构的timespec 结构，在这里它是：

I am using the struct timespec structure and here it is:

struct timespec {
           time_t tv_sec;                /* Seconds */
           long   tv_nsec;               /* Nanoseconds */
};

事情是，用户对于这些个人会员可以进入的值，我想提出一个检查的最大值。值的用户可以进入。

Thing is, user will be entering the values for each of these individual members, and i want to put a check a max. value the user can enter.

我能把最大。 time_t的的价值为int最大值？即 INT_MAX 为 tv_sec 和 LONG_MAX （在规定范围内确定。高）为 tv_nsec ？什么将是双方可接受的最低值？难道是零？我想负值不能接受？刚添加，这些值将是使用一个定时器。

Can I take the max. value of time_t as int max value? i.e INT_MAX for tv_sec and LONG_MAX (defined in limits.h) for the tv_nsec? What will be the minimum acceptable values for both? Is it zero? I guess negative values can't be accepted? Just to add, these values will be using in a timer.

P.S：哪里是为 time_t的 typedef的？找不到它time.h中。

P.S: Where is the typedef for time_t? Could not find it in time.h.

推荐答案

一个time_t的仅仅是一个长整型。结果
它的定义（在我的Ubuntu Linux系统）/usr/include/time.h，但是定义可以追溯到所有/usr/include/bits/types.h，其中 __ SLONGWORD_TYPE （这是 __ TIME_T_TYPE 定义为）的定义。

A time_t is simply a long int.
It's defined in (on my Ubuntu linux system) /usr/include/time.h, however the definition stretches back all the way to /usr/include/bits/types.h, where __SLONGWORD_TYPE (which is what __TIME_T_TYPE is defined to) is defined.

与检查简单，如果值大于问题，比方说， LONG_MAX ，是一旦值超过这个值就会自动环绕，成为负值。因此，你不能检查，看看是否有任何事情比这个值大 - 中宏定义为这种类型的可以采取的最大值

The problem with simply checking if a value is greater than, say, LONG_MAX, is that once a value exceeds this value it will automatically wrap around and become negative. Thus you can't check to see if anything is greater than this value - the macro is defined as the largest value this type can take.

您真的不希望用户输入这些值 - 除非用户你的意思是开发者。唯一真正的安全的方法来测试，这将是让用户输入一个字符串（C-风格，当然），然后运行两个检查：结果
1）检查如果用户输入更多的数字比允许的（一个廉价的窍门是 INT（LOG10（数字））+ 1 来计算一个号码的数字量）。结果
2）如果这是等于的数位，开始比较数字逐位。您可以通过使用模运算的一点点比较位数按位数。

You don't really want a user to input these values - unless by 'user' you mean 'developer'. The only real "safe" way to test this would be to let the user input a string (c-style, of course) and then run two checks:
1) Check to see if the user entered more digits than is allowed (a cheap trick is int(log10(number)) + 1 to count the amount of digits in a number).
2) If this is equal to the amount of digits, start comparing digit-by-digit. You can compare digit-by-digit by using a little bit of modulo arithmetic.

这是真的来检查用户是否输入一个数字，远远大过最安全的方式。你不会遇到任何问题的溢出这种方式，虽然它的是的繁琐得不得了。
希望这有助于。

This is really the safest way to check whether or not the user inputs a number that's far too large. You won't run into any overflow issues this way, though it is terrifically tedious. Hope this helps.

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