How do I pad a printf to take account of negative signs and variable length numbers?

Question

I'm trying to output some numbers in a log file and I want to pad a load of floats via the printf function to produce:

Currently I'm doing this:

printf("% 03.1f\n", myVar);

...where myVar is a float. The output from that statement looks like this:

58.0
20.0
38.0
-50.0
800.0
150.0
100.0

From what I've read I would expect my code to produce the output I mentioned at the top of this post, but clearly something is wrong. Can you only use one flag at a time? ..or is there something else going on here?

You probably should be using proper C++ streams for I/O if this is _really_ a C++ question. — paxdiablo, Mar 16 '11 at 12:38

score 32 · Accepted Answer · answered Mar 16 '11 at 12:23

32

The width specifier is the complete width:

printf("%05.1f\n", myVar);  // Total width 5, pad with 0, one digit after .

To get your expected format:

printf("% 06.1f\n", myVar);

answered Mar 16 '11 at 12:23

Erik

88,732
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198
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Yep, that's it. I hadn't realised the padding included the decimal point etc. ...although it needs to be 06 to include the space or sign value. – Jon Cage Mar 16 '11 at 12:24

score 1 · Answer 2 · answered Jan 18 '19 at 01:54

1

follows Erik, but I find

printf("% 6.1f\n", myVar);

also works.

answered Jan 18 '19 at 01:54

lumw

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How do I pad a printf to take account of negative signs and variable length numbers?

2 Answers2

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