how to use backslash as delimiter in c and C++?

Question

I have a string "abc\asd\zxc\12as", I want to use strtok() to split the string based on \\ delimiter. But having a \\ is treated as escape character. How can we handle this situation?

Also how can I get only the 3rd word(eg. zxc) from strtok()?

related/dupe: https://stackoverflow.com/questions/10220401/rules-for-c-string-literals-escape-character — NathanOliver, Jul 07 '21 at 12:17
Raw strings as shown by @Eljay or escaping the backslashes "\\"... — Aconcagua, Jul 07 '21 at 12:21
In C, you cannot split a string literal using `strtok` because attempted modification of the storage for the string literal results in *undefined behavior*. However, you can use the string literal as an initializer for an array of `char` and split the string in that array using `strtok`. — Ian Abbott, Jul 07 '21 at 12:28
In C++ exactly the same – solely that their type is `char const*` right from the start and you'd need to cast constness away to be able to provoke UB... — Aconcagua, Jul 07 '21 at 12:31
Apart from: Third argument: `char *w; for(unsigned int i = 0; i < 3; ++i, data = nullptr) { w = strtok(data, "\\"); if(!w) { /* error handling; make sure to abort loop appropriately */ } } /* use w */` — Aconcagua, Jul 07 '21 at 12:39
I highly recommend not using C-Style strings in C++. Also, the `strtok` cannot be used with a character string literal because `strtok` modifies its parameter string. — Thomas Matthews, Jul 07 '21 at 16:49

score 3 · Answer 1 · edited Jul 07 '21 at 15:56

3

Inside string literals in C and C++, you can use the \ character to refer to other characters that you can't type nicely in code - for example \n is understood to be the line feed character.

So for example the c-string "Hello\nWorld" if printed to the console would appear as

Hello 
World

Because of this in general the \ character needs to be escaped itself. For your example, this means using \\ in places where you might expect to use \. For example, this string "Hello\\World\\again" in the C source file would print as "Hello\world\again"

edited Jul 07 '21 at 15:56

Jonathan Leffler

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answered Jul 07 '21 at 12:21

Elemental

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i tried to fix the escaping but didnt get it right, ironically it isnt easy – 463035818_is_not_an_ai Jul 07 '21 at 12:23
@463035818_is_not_a_number thx - fixed it - was also surpried at how hard it was. – Elemental Jul 07 '21 at 12:24

score 0 · Answer 2 · edited Jul 07 '21 at 12:21

0

as string, \a means escaped a, escaping is usefull when you have chars like , newline(\n), tabs etc

what you need to do is escape de \ i.e. replacing them with \\

edited Jul 07 '21 at 12:21

463035818_is_not_an_ai

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answered Jul 07 '21 at 12:16

ΦXocę 웃 Пepeúpa ツ

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Steve Summit · Answer 3 · 2021-07-07T14:27:01.230

You just need to call something like strtok(string, "\\").

To get the third word, you'll have to call strtok three times:

#include <stdio.h>
#include <string.h>

int main()
{
    char string[] = "abc\\asd\\zxc\\12as";
    char *firstword = strtok(string, "\\");
    char *secondword = strtok(NULL, "\\");
    char *thirdword = strtok(NULL, "\\");
    printf("%s\n", thirdword);
}

Also, if you have any control over the data in this situation, you might want to choose a different delimiter character, since \ is going to be eternally inconvenient. Could you use | instead?

how to use backslash as delimiter in c and C++?

3 Answers3