Opening 2 data files with C++ - c++

Question

I wrote a program to create gnuplot commands according to data that was read from an input file. I required far too many commands to do this by hand. This worked quite nicely, but I now need to read data from two different data files and use these to create the gnuplot commands. Unfortunately something now seems to be going wrong with the reading of the two files. The portion of code involved in reading from the data files is as follows:
#include <iostream>
#include <fstream>
#include <sstream>
using namespace std;
int n_snapshots;
int main () {
std::cout << "Enter number of snapshots" << "\n";
std::cin >> n_snapshots;
int snap_cell_count[n_snapshots];
std::ifstream in_file_count("data/snapshot_data");
std::ifstream in_file_fates("data/cell_fates_data_final");
for (int i=0; i<n_snapshots; i++) {
in_file_count >> snap_cell_count[i];
}
in_file_count.close();
int cell_fates[snap_cell_count[n_snapshots-1]];
for (int i=0; i<snap_cell_count[n_snapshots-1]; i++) {
in_file_fates >> cell_fates[i];
}
in_file_fates.close();
n_snapshots is simply some integer, snap_cell_count[] is an array with "n_shapshots" elements, each of which takes a value read from the data file "snapshot_data". cell_fates[] is an array with a number of elements that is equal to the value of the last element in snap_cell_count[], and again the values of its elements are read from a file, in this case "cell_fates_data_final". The data files to be read from are stored in a folder called "data".
Unfortunately, the compiler returns the following errors.
Undefined symbols for architecture x86_64:
"std::basic_string<char, std::char_traits<char>, std::allocator<char> >::c_str() const", referenced from:
_main in ccrpSAv5.o
"std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >::str() const", referenced from:
_main in ccrpSAv5.o
"std::basic_istream<char, std::char_traits<char> >::operator>>(int&)", referenced from:
_main in ccrpSAv5.o
"std::basic_ostream<char, std::char_traits<char> >::operator<<(int)", referenced from:
_main in ccrpSAv5.o
"std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string()", referenced from:
_main in ccrpSAv5.o
"std::basic_ifstream<char, std::char_traits<char> >::close()", referenced from:
_main in ccrpSAv5.o
"std::basic_ifstream<char, std::char_traits<char> >::basic_ifstream(char const*, std::_Ios_Openmode)", referenced from:
_main in ccrpSAv5.o
"std::basic_ifstream<char, std::char_traits<char> >::~basic_ifstream()", referenced from:
_main in ccrpSAv5.o
"std::basic_ofstream<char, std::char_traits<char> >::open(char const*, std::_Ios_Openmode)", referenced from:
_main in ccrpSAv5.o
"std::basic_ofstream<char, std::char_traits<char> >::close()", referenced from:
_main in ccrpSAv5.o
"std::basic_ofstream<char, std::char_traits<char> >::basic_ofstream()", referenced from:
_main in ccrpSAv5.o
"std::basic_ofstream<char, std::char_traits<char> >::~basic_ofstream()", referenced from:
_main in ccrpSAv5.o
"std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >::basic_stringstream(std::_Ios_Openmode)", referenced from:
_main in ccrpSAv5.o
"std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >::~basic_stringstream()", referenced from:
_main in ccrpSAv5.o
"std::ios_base::Init::Init()", referenced from:
__static_initialization_and_destruction_0(int, int) in ccrpSAv5.o
"std::ios_base::Init::~Init()", referenced from:
__static_initialization_and_destruction_0(int, int) in ccrpSAv5.o
"std::cin", referenced from:
_main in ccrpSAv5.o
"std::cout", referenced from:
_main in ccrpSAv5.o
"std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)", referenced from:
_main in ccrpSAv5.o
"___gxx_personality_v0", referenced from:
Dwarf Exception Unwind Info (__eh_frame) in ccrpSAv5.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status
This is being compiled with the gcc compiler on Mac OSX Mountain Lion.
Does anyone have any idea what's wrong here?

Answer 1

Well, for starters you can't just say int snap_cell_count[n_snapshots] with the value of n_snapshots being determined at runtime. You have to do something like
int *snap_cell_count = new int[n_snapshots];
// do some stuff
delete[] snap_cell_count;
Same thing for cell_fates
As for your linker errors, maybe this question solves your issues...