警告C4244:“参数”:从“time_t”转换为“unsigned int”，可能丢失数据- c++。

I made a simple program that allows the user to pick a number of dice then guess the outcome... I posted this code before but with the wrong question so it was deleted... now I cannot have any errors or even warnings on this code but for some reason this warning keeps popping and I have no clue how to fix it... "warning C4244: 'argument' : conversion from 'time_t' to 'unsigned int', possible loss of data"

我做了一个简单的程序，让用户可以选择一些骰子，然后猜测结果…我之前发布了这个代码，但是错误的问题被删除了……现在我不能在这段代码上有任何错误甚至警告，但由于某种原因，这个警告一直在弹出，我不知道如何修复它……“警告C4244:‘参数’:从‘time_t’转换为‘unsigned int’，可能丢失数据”

#include <iostream>
#include <string>
#include <cstdlib>
#include <time.h>

using namespace std;

int  choice, dice, random;

int main(){
    string decision;
    srand ( time(NULL) );
    while(decision != "no" || decision != "No")
    {
        std::cout << "how many dice would you like to use? ";
        std::cin >> dice;
        std::cout << "guess what number was thrown: ";
        std::cin >> choice;
         for(int i=0; i<dice;i++){
            random = rand() % 6 + 1;
         }
        if( choice == random){
            std::cout << "Congratulations, you got it right! \n";
            std::cout << "Want to try again?(Yes/No) ";
            std::cin >> decision;
        } else{
            std::cout << "Sorry, the number was " << random << "... better luck next  time \n" ;
            std::cout << "Want to try again?(Yes/No) ";
            std::cin >> decision;
        }

    }
    std::cout << "Press ENTER to continue...";
    std::cin.ignore( std::numeric_limits<std::streamsize>::max(), '\n' );
    return 0;
}

This is what I am trying to figure out, why am I getting this warning: warning C4244: 'argument' : conversion from 'time_t' to 'unsigned int', possible loss of data

这就是我想要弄明白的，为什么我要得到这个警告:警告C4244:“参数”:从“time_t”转换为“unsigned int”，可能丢失数据。

4 个解决方案

#1

That's because on your system, time_t is a larger integer type than unsigned int.

这是因为在您的系统中，time_t是一个较大的整数类型，而不是unsigned int。

• time() returns a time_t which is probably a 64-bit integer.
• time()返回一个time_t，它可能是一个64位的整数。
• srand() wants an unsigned int which is probably a 32-bit integer.
• srand()需要一个无符号整数，它可能是一个32位的整数。

Hence you get the warning. You can silence it with a cast:

因此你得到了警告。你可以用演员来保持沉默:

srand ( (unsigned int)time(NULL) );

In this case, the downcast (and potential data loss) doesn't matter since you're only using it to seed the RNG.

在这种情况下，downcast(和潜在的数据丢失)并不重要，因为您只使用它来播种RNG。

#2

This line involves an implicit cast from time_t which time returns to unsigned int which srand takes:

这条线包含了来自time_t的隐式转换，时间返回到unsigned int, srand获取:

srand ( time(NULL) );

You can make it an explicit cast instead:

你可以把它变成一个明确的cast:

srand ( static_cast<unsigned int>(time(NULL)) );

#3

time() returns a time_t, which can be 32 or 64 bits. srand() takes an unsigned int, which is 32 bits. To be fair, you probably won't care since it's only being used as a seed for randomization.

time()返回一个time_t，它可以是32或64位。srand()取一个未签名的int，它是32位。公平地说，你可能不会在意，因为它只是被用作随机化的种子。

#4

This line involves an implicit cast from time_t which time returns to unsigned int which srand takes:

这条线包含了来自time_t的隐式转换，时间返回到unsigned int, srand获取:

srand ( time(NULL) );

You can make it an explicit cast instead:

你可以把它变成一个明确的cast:

srand ( static_cast<unsigned int>(time(NULL)) );