strcmp with string ending with newline

Question

I'm trying to write a C list filtering function that receives a country string, traverses the list and deletes all nodes with node->country == country. The problem is that node->country strings end with '\n' (because it's being read from a csv file) and therefore strcmp(node->country, country) never equals zero.

How would I solve this? I first thought about appending '\n' to country but that would probably raise more memory problems. Also thought about strstr but I don't really know how to work with that.

Thanks for any suggestions.

Why do *node->country strings* end with a newline? Can't you remove that before you store them in the list? — NathanOliver, May 25 '18 at 18:23
@returnNULL Search through the string and find the `'\n'` character and replace it with `'\0'` — Christian Gibbons, May 25 '18 at 18:39
@ChristianGibbons: Wasteful. If `node->country` begins with `'a'` but `country` begins with `'b'` - why bother? — einpoklum, May 25 '18 at 18:43
It is best to remove the newline retained by `fgets` *at the point of entry*. It might be unwise to input directly to the `struct` member. — Weather Vane, May 25 '18 at 19:38
Possible duplicate of [Removing trailing newline character from fgets() input](https://stackoverflow.com/questions/2693776/removing-trailing-newline-character-from-fgets-input/28462221#28462221) — Weather Vane, May 25 '18 at 19:50

score 2 · Accepted Answer · edited May 25 '18 at 18:40

2

As you are using strcmp, let's assume some C-style code:

node->country[strcspn(node->country, "\n")] = '\0';

This will alter your node->country value and terminate your string right before a new line (if any).

edited May 25 '18 at 18:40

melpomene

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answered May 25 '18 at 18:36

Stephan Lechner

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einpoklum · Answer 2 · 2018-05-25T18:57:50.697

0

Suggested alternatives:

Precompute

size_t len_of_country = strlen(country)

and use

(strncmp(country, node->country, len_of_country) == 0 &&
 (node->country[len_of_country] == '\n' || 
 node->country[len_of_country] == '\0'))

as the match criterion.

Same as (1.), but if the latter case, also set node->country[len_of_country] to 0 for later use.
Make your CSV parser chomp the trailing newline when reading the country string from the file, and just use strcmp().

edited May 25 '18 at 18:57

answered May 25 '18 at 18:41

einpoklum

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For option 3, how do I "chomp" the newline, using 1. ? – returnNULL May 25 '18 at 18:47
@returnNULL: Well, that depends on what you use to read you CSV file, which is a detail I don't have. If you're not using any library, consider doing so. There are at least [two](https://github.com/fiksu/rcsv/network) different [ones](https://github.com/robertpostill/libcsv/network) on GitHub and a (more classic?) [libcsv](https://sourceforge.net/projects/libcsv/), but I haven't tried them myself. – einpoklum May 25 '18 at 18:51
I tried option 1 with node->country = "France\n" and country = "France" and it returns 0, isn't it supposed to return 1? And the parser simply uses a strtok – returnNULL May 25 '18 at 18:56
@returnNULL: Oh, sorry, I mis-copy-pasted. I meant that after the `strncmp()` passes you also check the last character. See edit. – einpoklum May 25 '18 at 18:58

strcmp with string ending with newline

2 Answers2