int v/s. long in C

On my system, I get:

sizeof ( int )  = 4
sizeof ( long 开发者_如何学运维) = 4

When I checked with a C program, both int & long overflowed to the negative after:

a = 2147483647;
a++;

If both can represent the same range of numbers, why would I ever use the long keyword?

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int has a minimum range of -32767 to 32767, whereas long has a minimum range of -2147483647 to 2147483647.

If you are writing portable code that may have to compile on different C implementations, then you should use long if you need that range. If you're only writing non-portable code for one specific implementation, then you're right - it doesn't matter.

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Because sizeof(int)==sizeof(long) isn't always true. int normaly represents the fastest size with at least 2*8 Bit. long on the other hand is at least 4*8 Bit.

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C defines a number of integer types and specifies the relation of their sizes. Basically, what it says is that sizeof(long long) >= sizeof(long) >= sizeof(int) >= sizeof(short) >= sizeof(char), and that sizeof(char) == 1.

But the actual sizes are not defined, and depend on the architecture you are running on. On a 32-bit PC, int and long are typically four bytes and long long is 8 bytes. But on a 64-bit system, long is typically 8 bytes, and thus different from int.

There is also a type called uintptr_t (and intptr_t) that is guaranteed to have the same size as data pointers.

The important thing to remember is to not assume that you can, for example, store pointer values in a long or an int. Being portable is probably more important than you think, and it is likely that you will want to compile your code on a 64-bit system in the near future.

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I think it's more of a compiler issue nowadays, since computers has gone much faster and demands more numbers, as was the case before.

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On different platform or with a different compiler, the int and long may be different. If you don't plan to port your code to anything else or use a different machine, then pick the one you want, it won't make a difference.

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It depends on the compiler, and you might want to check this out: What does the C++ standard state the size of int, long type to be?

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The size of built-in data types is variable depending on the C implementation, but they all have minimum ranges. Nowadays, int is typically 4 bytes long (32-bits) because most OS are 32-bit. Note that char will always be 1 bytes.

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The size of a data type depends upon the compiler. Different compilers have diffrent size of int and other data types.

So if you make a code which is going to run on diffrent machine you should use long or it is depend on the range of the value tha t ur variable may have.