problem in allocating memory in linux

Question

i signed with stars the 2 rows that are creating the problem.

the first row allocates memory for logfile, that will be used in the second signed row. at the second signed row there is a problem of segmentation fault. This is caused by the fact that "logfile" is not allocated. I'm am sure of this because if i allocate the memory in load() it works. However I want to allocate the memory in the constructor of the class and not in the method load().

I cannot understand why it does not work! This is my first time on linux and so maybe i'm doing something wrong!

Thank you, Marco

    server::server(){
    port = 0;
    serverup = 0;
    loaded = 0;
    logfile = (char *) malloc(SERVER_PATHS_SIZE*sizeof(char)); //**************************** 
}

int server::load(int in_id, char *in_name, char *in_ip, int in_port,
                 char *in_rcon, char *in_logfile){

    int err;

    sprintf(name, "%s\x00", in_name);
    sprintf(ip, "%s\x00", in_ip);
    port = in_port;
    sprintf(rcon, "%s\x00", in_rcon);
    sprintf(logfile,"%s\x00", in_logfile); //**********************************

    err = urt.set(ip, port, rcon);
    if(err < 1){
        printf("server::load(): error from urt.set()\n");
        return 0;
    }

    printf("server::load(): server %d loaded!\n", id);
    loaded = 1;

    return 1;
}

Please reduce your code to a working (i.e. compilable, runnable) example that demonstrates the problem. Otherwise we can only guess where the problem is... — sleske
– sleske, Commented Apr 21, 2011 at 12:06
We cannot see where logfile is declared. Is it a member variable of class server? Is it global? Making your examples stand-alone compilable is crucial for debugging. — DevSolar
– DevSolar, Commented Apr 21, 2011 at 12:20
when programming c++, new is usually preferred over malloc — knittl
– knittl, Commented Apr 21, 2011 at 12:26
Consider removing the "linux" tag from this topic as it has nothing to do with Linux. — MarkR
– MarkR, Commented Apr 21, 2011 at 14:00

sehe · Accepted Answer · 2011-04-21 12:19:42Z

4

I think you are trying to nullterminate in_logfile and in_rcon

This won't work with printf because printf requires null-terminated string as arguments to %s in the first place.

charptr[known_length] = 0

instead

answered Apr 21, 2011 at 12:19

sehe

401k49 gold badges475 silver badges674 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Lightness Races in Orbit Over a year ago

To eleborate a little, the segmentation fault occurs because the lack of null-termination in the original input to sprintf causes data way past the end of the original input to be read, causing invalid reads. Further, you're then trying to assign lots more data to the output arrays than you think, causing invalid writes.

Tristram Gräbener · Accepted Answer · 2011-04-21 12:26:46Z

1

This is definitely not an answer, but developping in C++ will help you to avoid the memory problems you get with your C-with-classes code.

Use std::strings, then copying them will be trivial (compared to sprintf), and it will be way more safe. Using the deprecated char* makes things way to confusing.

A nice side effect is that you won't need to do manual allocation of the memory (with malloc or new), and eliminating any risk of memory leak.

answered Apr 21, 2011 at 12:26

Tristram Gräbener

9,7313 gold badges38 silver badges50 bronze badges

1 Comment

Lightness Races in Orbit Over a year ago

Using char* to handle character arrays is not deprecated. (Though binding string literals to char* rather than char const* is.)

Dark Falcon · Accepted Answer · 2011-04-21 12:16:16Z

0

I don't see the destructor of the server class. Do you have a destructor that frees the memory?
I don't see the code which creates and uses the server object. Could it be that you create the server object but then make a copy of it, and the problem occurs because you do not properly implement copying semantics?

answered Apr 21, 2011 at 12:16

Dark Falcon

44.2k6 gold badges91 silver badges104 bronze badges

3 Comments

Lightness Races in Orbit Over a year ago

(2) No, it couldn't, because of (1). :)

Marco Over a year ago

Dark Falcon, you are a genius!! That was the problem!! Many thanks!

Marco Over a year ago

Basically the constructor was not called... probably i was creating the server object in a wrong way! thanks to all for the replies!

Collectives™ on Stack Overflow

problem in allocating memory in linux

3 Answers 3

1 Comment

1 Comment

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

1 Comment

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related