#145 partial strings
Learning how printf can be instructed to select a limited number of characters from a string.
Notes
I learned of this from the Embedded Artistry blog. It could be useful when dealing with string buffers that are not null terminated.
Basically: the width parameter of the format string applies also the string.
e.g. %.5s limits output to a maximum of 5 characters:
const char * mystr = "... long string ...";
printf("Just 5 characters: %.5s\n", mystr);
Or the * width specifier can be used to take the length as an argument:
printf("Just 5 characters: %.*s\n", 5, mystr);
This also works with related functions such as sprintf.
Demo
demo.c exercises various string format combinations. Use make to compile and run:
$ make
gcc -Wall -O0 demo.c -o demo
./demo
===== test_explicit_printf_format
> printf("Prints just 5 characters (should print 'ABCDE'): %.5s\n", long_string);
Prints just 5 characters (should print 'ABCDE'): ABCDE
===== test_printf_width_as_argument
> printf("Prints just %d characters (should print 'AB'): %.*s\n", 2, 2, long_string);
Prints just 2 characters (should print 'AB'): AB
===== test_explicit_printf_format
> printf("Asking for 5 characters, but only 4 available (should print 'ABCD'): %.5s\n", short_string);
Asking for 5 characters, but only 4 available (should print 'ABCD'): ABCD
===== test_explicit_sprintf_format
> sprintf(result, "%.5s", long_string);
===== test_sprintf_with_width_as_argument
> sprintf(result, "%.*s", 2, long_string);