c++ seg fault:

[Carlis]

Hi

I am trying to run the below code. I get '1102 Segmentation fault'. I added some cout's for the purpose of tracing. I get the "file open " but not the "getline". So I think the error occurs on the while(...) line.

The lines in the file contains approx 10,000 characters each, so I am wondering if this is to much to be stored in the string, hence the seg fault. Can anyone tell me how to fix this?

Regards, Carlis







void Iteration::importConfig(char *file){
using namespace std;
ifstream indata;
cout << "opening file"<< endl;
indata.open(file);
cout << "file open"<< endl;
string sLine;
int row=0;
int subrow;
while(getline(indata,sLine)){ \\ seg fault occur here
cout << "getline";
do stuff
}
}

 

[EagleKeeper]

The std string container will hold only a few thousand bytes.

You will have to modify and/or override the storage capacity

 

[Carlis]

hm? I tried two thinks to find out the cause. First I tried using a smaller file, and then it worked fine, so this is clearly the problem.

I also tried running it with the large file, but first doing >> sLine.resize(50000); <<. This did however not solve the problem. Could it be that the method itself does not accept such large chunks of data?

 

[SunnyD]

To find out how much a container class can hold, use the max_size() member function of that container, which will return a value of type size_type (of that class).

 

[Kirby]

http://www.cplusplus.com/refer...tring/string/max_size/ shows max_size to be 4294967291, and I got 4294967294 on my machine.

 

[GodlessAstronomer]

I would suggest using a regular char* instead of a string, like an old school C string. No limits on size (except how much memory you have). If you're not comfortable doing that then try Googling, there is bound to be a large string library out there somewhere.

 

[Venix]

Do you have exceptions off or something? If it were an issue of std::string trying to allocate a buffer that's too large, it would throw std::bad_alloc, not cause a segfault.

"getline" won't necessarily be shown immediately because you don't flush the output buffer. So it's likely that the code does go into the loop, and your "do stuff" code breaks something. Flush the output buffer (<< endl or << flush will do it) or use a debugger to determine where it's crashing.

 

[postmortemIA]

i would pre-initialize char* array to large size

also what's wrong with using fopen to read files?

 

[degibson]

If you really suspect your string implementation (a likely culprit, as I recall a previous thread), try running this:

(not, remove the ~'s before running... I added them for horiz. whitespace)

std::string s;
for(unsigned int i = 0; i < UINT_MAX; ++i) {
~~cout << "Len: " << s.length() << endl;
~~s += s;
~~s += "foo";
}

If it dies with Len: ~10,000, you have your culprit.

 

[mozartrules]

What getline() function are you calling here (I cannot see since you are not showing your includes)?

The only recognized standard C++ getline() functions are members of class istream, but those aren't the ones you are calling.

But neither of the getline() functions http://www.cplusplus.com/refer...tream/istream/getline/ take a string as arguments, so you have to make a buffer yourself. The standard stream class and the iostream library are not really integrated.

Back to the original question, a string has no limits other than what is imposed by your system (Windows in particular doesn't like it when you allocate close to the available memory, so running programs like the one suggested by degibson tends to force an eventual hard reboot), but this runs well enough on Visual Studio 2008

#include <string>

int main(int argc, char** argv)
{
std::string str;
str.resize(1000000, 'A');

return 0;
}

Also, be const correct and make your argument 'const char *file' or better 'const char *filename', informative names too important.

 

[mozartrules]

Originally posted by: postmortemIA
i would pre-initialize char* array to large size

also what's wrong with using fopen to read files?

1. Using fixed size char arrays is not good programming practice and a heap allocation forces you to remember to free it even in the presence of exceptions.

2. Similar comment, we left ::fopen() to the history books when the ANSI C++ standard came out in 1998. It forces you to remember to close the file.

 

[Templeton]

Originally posted by: mozartrules
What getline() function are you calling here (I cannot see since you are not showing your includes)?

The only recognized standard C++ getline() functions are members of class istream, but those aren't the ones you are calling.

But neither of the getline() functions http://www.cplusplus.com/refer...tream/istream/getline/ take a string as arguments, so you have to make a buffer yourself. The standard stream class and the iostream library are not really integrated.

Back to the original question, a string has no limits other than what is imposed by your system (Windows in particular doesn't like it when you allocate close to the available memory, so running programs like the one suggested by degibson tends to force an eventual hard reboot), but this runs well enough on Visual Studio 2008

#include <string>

int main(int argc, char** argv)
{
std::string str;
str.resize(1000000, 'A');

return 0;
}

Also, be const correct and make your argument 'const char *file' or better 'const char *filename', informative names too important.

std::getline(std::istream&, std::string&) is defined in <string>, there's no need to allocate and manage your own buffer in this case.

I'll second the post above in doubting that this is really seg-faulting in getline due to allocation issues, Have you tried stepping through the code with a debugger?