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[C++] Avoiding crash with atoi()

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Reak
I post too much

Reputation: 0

Joined: 15 May 2007
Posts: 3496

Posted: Fri Apr 25, 2008 3:42 pm Post subject: [C++] Avoiding crash with atoi()

Hello,

I'm having a problem, I'm coding !warpplayer <username> <mapid> for TitanMS atm.
Here's the code so far:

Code:

if(strcmp(command, "warpplayer") == 0){
   if(strlen(next_token) > 0){
      printf("test2 \n");
      char* name = strtok_s(NULL, " ",&next_token);
         for (hash_map <int, Player*>::iterator iter = Players::players.begin(); iter != Players::players.end(); iter++){
            if(strcmp(iter->second->getName(), name) == 0){
                     printf("test1 \n");
                     char* mapstr = strtok_s(NULL, " ",&next_token);
                     printf("test2 \n");
                     printf("%s \n", mapstr);
                     if(strlen(mapstr) > 0 && mapstr != NULL)
                     {
                        int map = atoi(mapstr);
                        printf("test3 \n");
                        if(Maps::info.find(map) != Maps::info.end())
                           Maps::changeMap(player, map, 0);
                        printf("test4 \n");
                     }
            }
         }
      }
   }

But if someone does only enter "!warpplayer <username>" without the mapid, the server will crash.
It crashes because it tries to convert mapstr (which is NULL then) to an integer by using atoi. But why does it continue even if i check with "if(strlen(mapstr) > 0 && mapstr != NULL)" ?

Help please.

Noz3001
I'm a spammer

Reputation: 26

Joined: 29 May 2006
Posts: 6220
Location: /dev/null

Posted: Fri Apr 25, 2008 3:50 pm Post subject:

Code:

if( mapstr )
{

}

Try that first see if it still continues.

lurc
Grandmaster Cheater Supreme

Reputation: 2

Joined: 13 Nov 2006
Posts: 1900

Posted: Fri Apr 25, 2008 3:53 pm Post subject:

Make sure in the beggining that there are 3 tokens? if there is to little or to much have it say some error. _________________

Reak
I post too much

Reputation: 0

Joined: 15 May 2007
Posts: 3496

Posted: Fri Apr 25, 2008 3:58 pm Post subject:

noz3001 wrote:

Code:

if( mapstr )
{

}

Try that first see if it still continues.

Works perfect, didn't know about this. Thank you!

@lurc: Also thanks to you, but it noz's tip works great.

Jani
Grandmaster Cheater

Reputation: 2

Joined: 29 Dec 2006
Posts: 804

Posted: Sat Apr 26, 2008 5:16 am Post subject:

You should not be using atoi, there's your reason :P

I suggest you to use either a stringstream or strtol:

Code:

#include <iostream>
#include <sstream>

int main(int argc, char *argv[])
{
if( argc < 2)
   return EXIT_FAILURE;

std::stringstream temp;
temp << argv[1];
long int i;
char *flag;

if( temp >> i )
   std::cout << "ss: " << i << std::endl;

i = strtol( argv[1], &flag, 10 );
if( flag != argv[1] )
   std::cout << "strtol: " << i << std::endl;

return EXIT_SUCCESS;
}

The number is taken as an argument and it's only printed if the conversion was successful (ie. there's at least one number in the front.)

decheatengine
Cheater

Reputation: 0

Joined: 10 Jun 2007
Posts: 25

Posted: Sat Apr 26, 2008 9:07 am Post subject:

Quote:

if(strlen(mapstr) > 0 && mapstr != NULL)

It crashed because you try to find the length of the NULL. You could try

if (mapstr!=NULL && strlen(mapstr) > 0)

since I believe C will only do the test for both cases if the first test is TRUE. If the first test is FALSE, the second test will not be carry out. They called this short circuit or something. For cases that has || (or), if the first case is TRUE, the subsequent test are skipped.

Reak
I post too much

Reputation: 0

Joined: 15 May 2007
Posts: 3496

Posted: Sun Apr 27, 2008 7:46 am Post subject:

decheatengine wrote:

Quote:

if(strlen(mapstr) > 0 && mapstr != NULL)

Yea I did that, check my main post Very Happy

I got it working already. Thanks anyway Smile

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