Formatting text with printf or printstring in C

Question

I want to print text to a terminal program from a microcontroller, something like this:

printString("textline one here: OK\n"); printString("textline two here that is longer: OK\n"); printString("textline three here that is even longer: OK\n");

How do I make the text to always be in columns even if I decide to change the textline? To avoid that it looks something like this in the printout in the terminal program:

textline one here: OK textline two here that is longer: OK textline three here that is even longer: OK

and more like this (without having to add extra spaces in text and double check in the terminal program how it looks for every change I do to any text) :

textline one here: OK textline two here that is longer: OK textline three here that is even longer: OK

Is it easier to use printf or printstring for this?

Use a fixed width. printf("%-80s%s\n", "text one line", "OK") — William Pursell
– William Pursell, Commented Jan 15, 2020 at 17:15
The section here on format placeholders has some useful information about the flags you can use to format your string: en.wikipedia.org/wiki/Printf_format_string — kennyvh
– kennyvh, Commented Jan 15, 2020 at 17:17
I'd suggest leaving a couple of spaces between the conversion specifications in printf("%-75s %s\n", message, status); so that even if the message is longer than the specified length (75 here), you get separation between the string and the status. Alternatively, tell printf() to truncate the message: printf("%-75.75s %s\n", message, status);. You could change the lengths dynamically; replace the 75 values with * and pass an int argument before the value: printf("%-*.*s %s\n", 75, 75, message, status);. — Jonathan Leffler
– Jonathan Leffler, Commented Jan 15, 2020 at 17:32

dbush · Accepted Answer · 2020-01-15 17:57:40Z

Rather than including the first part of the text directly in your printf format string, pass it as a parameter to the %s format specifier. You can then add a field width to it to specify the minimum number of characters to print as well as the - flag to tell it to left-justify.

For example, this code:

printf("%-50s %s\n", "textline one here:", "OK"); printf("%-50s %s\n", "textline two here that is longer:", "OK"); printf("%-50s %s\n", "textline three here that is even longer:","OK");

Prints:

textline one here: OK textline two here that is longer: OK textline three here that is even longer: OK

Also, you could use * instead of an a explicit field width to pass it in as a parameter. That way if you need to change the column width you only do it in one place:

int width = 50; printf("%-*s %s\n", width, "textline one here:", "OK"); printf("%-*s %s\n", width, "textline two here that is longer:", "OK"); printf("%-*s %s\n", width, "textline three here that is even longer:","OK");

@mannen Glad I could help. Feel free to accept this answer if you found it useful.

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