Using String Size to Declare Array Size in C?

Question

Lets say I have two string sizes sizeA and SizeB, can I use them both to create an array like the following:

    char str[sizeA+sizeB];

I want the array to be one dimensional and with size of both sizeA and sizeB combined. How would I do that correctly?

Thank you!

Is that array definition inside a code block, making the array local? Then, if the compiler/library supports it alloca may be your best bet (given typical string lengths). — Peter - Reinstate Monica
– Peter - Reinstate Monica, Commented May 23, 2014 at 14:27

unwind · Accepted Answer · 2014-05-23 14:22:09Z

2

Yes, that's fine.

It's called a variable-length array and was added in C99.

If you intend to create an actual string in that array, you need to + 1 for the terminator.

If this is inside a function and you intend to return the new array, you must use heap allocation through malloc().

edited May 23, 2014 at 14:22

answered May 23, 2014 at 14:00

unwind

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Comments

alain · Accepted Answer · 2014-05-23 14:19:50Z

1

If you use a compiler that does not support C99, and sizeA and sizeB are not constant, you can not do that. You could either determine a size that will be big enough for all cases, or you can dynamically allocate the buffer with the correct size using malloc

edited May 23, 2014 at 14:19

answered May 23, 2014 at 14:02

alain

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