C: Get substring before a certain char

Question

For example, I have this string: 10.10.10.10/16

and I want to remove the mask from that IP and get: 10.10.10.10

How could this be done?

You can combine `std::string::substr()` and `std::string::find()` — Andy Prowl, Feb 21 '13 at 15:41
if you're ok with destroying the original string, you can use `strchr('/') = '\0'` — aragaer, Feb 21 '13 at 15:42
C or C++. The answer for one is not necessarily valid for the other language. — pmg, Feb 21 '13 at 15:45

score 34 · Answer 1 · answered Feb 21 '13 at 15:43

34

Here is how you would do it in C++ (the question was tagged as C++ when I answered):

#include <string>
#include <iostream>

std::string process(std::string const& s)
{
    std::string::size_type pos = s.find('/');
    if (pos != std::string::npos)
    {
        return s.substr(0, pos);
    }
    else
    {
        return s;
    }
}

int main(){

    std::string s = process("10.10.10.10/16");
    std::cout << s;
}

answered Feb 21 '13 at 15:43

Andy Prowl

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Im really sorry, c is what i need – Itzik984 Feb 21 '13 at 15:46
thanks for the help i needed for a cpp projetct ! – Tsirsuna Feb 08 '22 at 09:50

score 18 · Accepted Answer · edited Apr 07 '20 at 23:23

18

Just put a 0 at the place of the slash

#include <string.h> /* for strchr() */

char address[] = "10.10.10.10/10";
char *p = strchr(address, '/');
if (!p)
{
    /* deal with error: / not present" */
    ;
}
else
{
   *p = 0;
}

I don't know if this works in C++

edited Apr 07 '20 at 23:23

Simson

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answered Feb 21 '13 at 15:47

pmg

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8

wasted memory! all 3 bytes of it! – 75inchpianist Feb 21 '13 at 15:56
1

@75inchpianist What do you mean by that? Where is the memory "wasted" and how? – Feb 21 '13 at 16:34
Shouldn't this be `*p = '\0';` – squareborg Feb 25 '15 at 17:03
3

@Shutupsquare: except in source form, `'\0'` and `0` are absolutely identical. The first is a literal character: it has type `int` and value `0`; the second is a literal integer: it has type `int` and value `0`. *Things may be different in C++. I don't know that language.* – pmg Feb 25 '15 at 19:13

score 3 · Answer 3 · edited Sep 13 '17 at 16:16

3

char* pos = strstr(IP,"/"); //IP: the original string
char [16]newIP;
memcpy(newIP,IP,pos-IP);   //not guarenteed to be safe, check value of pos first

edited Sep 13 '17 at 16:16

Goldie

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answered Feb 21 '13 at 15:43

75inchpianist

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nav · Answer 4 · 2019-04-24T13:39:00.377

1

Example in C++

#include <iostream>
using namespace std;

int main() 
{
    std::string addrWithMask("10.0.1.11/10");
    std::size_t pos = addrWithMask.find("/");
    std::string addr = addrWithMask.substr(0,pos);
    std::cout << addr << std::endl;
    return 0;
 }

edited Apr 24 '19 at 13:39

answered Mar 10 '17 at 18:52

nav

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Olaf Dietsche · Answer 5 · 2013-02-21T16:13:46.127

0

Example in c

char ipmask[] = "10.10.10.10/16";
char ip[sizeof(ipmask)];
char *slash;
strcpy(ip, ipmask);
slash = strchr(ip, '/');
if (slash != 0)
    *slash = 0;

edited Feb 21 '13 at 16:13

answered Feb 21 '13 at 15:47

Olaf Dietsche

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score 0 · Answer 6 · answered Feb 21 '13 at 15:48

I see this is in C so I guess your "string" is "char*"?
If so you can have a small function which alternate a string and "cut" it at a specific char:

void cutAtChar(char* str, char c)
{
    //valid parameter
    if (!str) return;

    //find the char you want or the end of the string.
    while (*char != '\0' && *char != c) char++;

    //make that location the end of the string (if it wasn't already).
    *char = '\0';
}

C: Get substring before a certain char

6 Answers6

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