IDL out of the for loop

最新推荐文章于 2023-03-10 17:05:43 发布

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本文探讨了在使用ID Lisold编程时，16位整数限制导致的FOR循环问题，特别是当循环变量超过32768时出现的负数情况。提供了解决方案，包括将循环变量更改为长整型，以避免超出范围的问题。

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IDL is old. Grandfatherly, even. When it was first written, you had a really souped-up computer if you had added an additional 10 MByte hard drive to go with the standard 1 MByte of disk space. So, you can maybe understand why the default integer size in IDL is 16-bits, or two bytes. This is a short integer by any current standards. This causes problems because a 16-bit signed integer can only represent the values -32768 to 32768. Occasionally, you need an integer larger than that, and even throwing in fingers and toes doesn't do the job.

One place where it causes problems is when short integers are used as counters in FOR loops.

    FOR j=0,n DO ...

If you want your loop to go beyond 32768 (loop values will become negative it they go beyond their bounds), you will have to make your loop variable a long integer, like this.