How to print a string using printf without it printing the trailing newline

Question

I'm trying to print some strings using printf() but they are ~~null terminated~~ having trailing newline and that messes with the formating:

printf("The string \"%s\" was written onto the file \"%s\"", str, fname);

Say the string contains "The Racing car." and the file name is "RandomText1.txt" This prints:

The string "The Racing car.
" was written onto the file "RandomText1.txt
"

However I want it to print in just one line:

The string "The Racing car." was written onto the file "RandomText1.txt"

I know I can modify the strings to get rid of the ~~null terminator~~ newline but I'd like a way, if possible, to achieve this output without modifying the strings.

Is it possible?

They're __not__ null-terminated, they have a beeline char at the end — ForceBru, May 15 '15 at 13:42
Sorry, I'm a bit of a newbie to programming. I thought the \n was the null terminator — Tiagofer, May 15 '15 at 13:49
@ForceBru I think your words are _a little_ misleading, they __are__ null-terminated and having a `\n` before the null-termination, IMHO :-) — Sourav Ghosh, May 15 '15 at 14:05
@SouravGhosh, yes, you're certainly right. I meant, the null-termination wasn't the problem here. — ForceBru, May 15 '15 at 15:42

Sourav Ghosh · Accepted Answer · 2015-05-15T14:02:38.787

10

This has nothing to do with the null terminator. a string must be null-terminated.

You're facing issues with the trailing newline (\n) here. you have to strip off that newline before passing the string to printf().

Easiest way [requires modification of str]: You can do this with strcspn(). Pseudo code:

str[strcspn(str,"\n")] = 0;

if possible, to achieve this output without modifying the strings.

Yes, possible, too. In that case, you need to use the length modifier with printf() to limit the length of the array to be printed, something like,

printf("%15s", str);  //counting the ending `.` in str as shown

but IMHO, this is not the best way, as, the length of the string has to be known and fixed, otherwise, it won't work.

A little flexible case,

printf("%.*s", n, str);

where, n has to be supplied and it needs to hold the length of the string to be printed, (without the newline)

edited May 15 '15 at 14:02

answered May 15 '15 at 13:43

Sourav Ghosh

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Sorry, I'm a bit of a newbie to programming. I thought the \n was the null terminator – Tiagofer May 15 '15 at 13:45
1

@Tiagofer Nevermind, happens. BTW, you should check my updated answer. :-) – Sourav Ghosh May 15 '15 at 14:01
1

I had to go away for a while so I just had the oportunity to look at your updated answer now. It's awesome, thank you! :D – Tiagofer May 15 '15 at 17:14

Mark Segal · Answer 2 · 2019-11-18T13:41:42.750

7

As already pointed out, every string in C should be null-terminated (else - how could printf know where the string ends?)

You need to search the array for new-lines, presumably using strchr.

Try this:

  char* first_newline = strchr(str, '\n');
  if (first_newline)
      *first_newline = '\0';

It will terminate the string at the first instance of a newline.

edited Nov 18 '19 at 13:41

answered May 15 '15 at 13:46

Mark Segal

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@iharob right, but somehow it does not answer the question `without modifying the strings`, as requested by OP. but then again, it's accepted, so.. Peace :-) – Sourav Ghosh May 15 '15 at 13:58

score 1 · Answer 3 · edited May 23 '17 at 12:06

1

EDIT: Take a look at this ;)

How to print only certain parts of a string?

You'll just have to print 'strings lenths - 1' characters

edited May 23 '17 at 12:06

Community

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answered May 15 '15 at 13:42

Guillaume Munsch

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score 1 · Answer 4 · answered May 15 '15 at 13:55

It seems that you read data in array str using standard function fgets (or some other method) that includes in the string also the new line character '\n' that coresponds to Enter key.

You shoud remove this character. This can be done the following way

size_t n = strlen( str );

if ( n && str[n-1] == '\n' ) str[n-1] = '\0';

How to print a string using printf without it printing the trailing newline

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