CODEWITHSUNDEEP
carraysstringchar
Nathan
Nathan

Reputation: 360

How to add "\n" at the end of a string in C

I know how to do it on the string, so "hello world" would be "hello world\n". But if I have something like char *str = "helloworld". and I want to add \n at the end of str, how am I supposed to do it?

Upvotes: 5

Views: 24544

Answers (3)

GriffithLea
GriffithLea

Reputation: 63

As others have pointed out, you can't add/concatenate more characters to the end of str in your code example without some form of reallocation of space.

But if I may respond to what might be the real aim of your question (you asked specifically about appending a newline and not just any text, which makes me think you are trying to format text for output), you can easily add '\n' alongside str when you send it to stdout:

printf("%s\n", str);

In fact, you can prepend/append whatever you like before/after str by altering the format string:

printf(">>> %s <<<\n", str);

printf() has lots of "friends", e.g. fprintf() for outputting to a file instead of stdout, that behave similarly.

This way, you don't need to worry about reallocating anything just to append a newline or otherwise format the text for output.

Does that help?

Upvotes: 0

Abhishek Keshri
Abhishek Keshri

Reputation: 3234

You have declared string literals, which cannot be modified. You will need to do something like:

char *str;
str = malloc (sizeof (char) * MAX_SIZE);
strcpy (str, "HelloWorld");
strcat (str, "\n");

or, You should use an array.

Upvotes: 2

Barmar
Barmar

Reputation: 780869

You can't do this.

When you use

char *str = "helloworld";

str points to a string that cannot be modified. It also doesn't have any extra space available beyond the characters in the literal, so you can't extend its size.

If you need a string that's the same as str but with an added newline, you need to make a copy first.

char *newstr = malloc(strlen(str) + 2);
strcpy(newstr, str);
strcat(newstr, "\n");

Remember to add 2 to the length: 1 byte for the newline being added, another for the trailing null.

See Why do I get a segmentation fault when writing to a string initialized with "char *s" but not "char s[]"? for more information about the differences between using 

char str[] = "helloworld";

and

char *str = "helloworld";

Upvotes: 12

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