Using snprintf to print an array? Alternatives?

Question

Is it at all possible to use snprintf to print an array? I know that it can take multiple arguments, and it expects at least as many as your formatting string suggests, but if I just give it 1 formatting string and an array of values, will it print the entire array to the buffer?

The reason I ask, is because I am modifying source code, and the current implementation only supported one value being placed in a string, but I am modifying it to support an array of values. I want to change the original implementation as little as possible.

If this doesn't work, is there another way someone would recommend to do this? Should I just suck it up and use a for loop (how well would that really work without stringbuffers)?

Essentially: What would be the best way to get all of the values from an array of doubles into the same string for a return?

Answer 1

No, there's no formatting specifier for that.

Sure, use a loop. You can use snprintf() to print each double after the one before it, so you never need to copy the strings around:

double a[] = { 1, 2, 3 };
char outbuf[128], *put = outbuf;

for(int = 0; i < sizeof a / sizeof *a; ++i)
{
  put += snprintf(put, sizeof outbuf - (put - outbuf), "%f ", a[i]);
}

The above is untested, but you get the general idea. It separates each number with a single space, and also emits a trailing space which might be annoying.

It does not do a lot to protect itself against buffer overflow, generally for code like this you can know the range of the inputs and make sure the outbuf is big enough. For production code you would need to think about this of course, the point here is to show how to solve the core problem.