CODEWITHSUNDEEP
c++arraysfstream
Christine.L
Christine.L

Reputation: 1

Array of fstream in C++

I'm writing an algorithm with NTL library(it's a C++ library). Now I have N files to edit and I have to create/open them at the same time. I try to dynamically allocate space for the N file pointers but there's something wrong with the code. The code snippet is shown below:

P1 = (char **)calloc(n+1, sizeof(char *));//P1 is used to save file names
for(i=1; i<=n; i++)
{
    P1[i]=(char *)calloc(20, sizeof(char ));
    sprintf(P1[i],"P1_%d.txt",i);
}
ifstream *fin = (ifstream *)calloc(n+1, sizeof(ifstream));
for(i=1; i<=n; i++)
{
    fin[i].open(P[i]);
}

When the program runs in linux, it tells me there is a Segmentation Fault.

Since N is not larger than 200, when I try to use

ifstream fin[200]

instead of

ifstream *fin = (ifstream *)calloc(n+1, sizeof(ifstream));

the program runs.

I just learned C but not C++, and I don't really know how the fstream class works. Could you tell me if there is some better ways to open N files at the same time?

Upvotes: 0

Views: 1518

Answers (1)

ForEveR
ForEveR

Reputation: 55887

calloc will just alloc memory, but ifstream is complex type. It has constructor, that should be called on object creation. I think you should read some docs/book about C++. You should allocate memory in C++ using new expression. Btw, it's better to use smart pointers (such as unique_ptr) if you use modern C++ compiler. Also, it's much better to use vector, when you want to store unknown on compile-time count of objects. In this case it will be simpler to just use vector<ifstream>.

// includes for vector and unique_ptr.
#include <vector>
#include <memory>

vector<ifstream> streams;
for (int i = 0; i < n; ++i)
{
   streams.push_back(ifstream(P[i]));
}

Upvotes: 5

Related Questions