Help please ! (Segmentation fault while sorting a vector)

[jwlkr]

Hi,
I am trying to sort a vector of a user defined type: a class which represents points in cartesian coordinates. The vector of points needs to be sorted according to the value of the x-coordinate. I am trying to use the "sort" function defined in algorithms.h and I am getting a segmentation fault. I have inlined the code below. Can someone please tell me what I am doing wrong ? I am compiling this code on linux ( fedora 6 x86_64 using gcc 4.0)
-
Many thanks
JWalker
PS: I am just learning C++ and STL perhaps I am making some fundamental mistake.
=============== =============== =============== ==========
#include <iostream>
#include <fstream>
#include <iterator>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
class _vertex{
public:
double x;
double y;
double z;
_vertex() {x=0.0, y =0.0; z =0.0;}
_vertex(double xa,double ya, double za){x=xa; y =ya; z=za;}
_vertex (const _vertex & b) {x = b.x; y=b.y; z=b.z;}
};

bool sortbyx(const _vertex& v1,const _vertex& v2){
if(v1.x<=v2.x)
return true;
else
return false;
}

void print(const _vertex& tmp){
cout<<tmp.x<<"\ t"<<tmp.y<<"\t" <<tmp.z<<"\t"<< endl;
}

int main(){
vector<_vertex> nodes;

// read node information from files in vector "qvolist"
vector<string> qvolist;
qvolist =Read_qvofile_l ist("temp.txt") ;
for(int i =0; i<qvolist.size( );i++){
ifstream qvofile;
string line;
int Nvertices, NFaces, NEdges;

qvofile.open((q volist.at(i)).c _str());
cout<<(qvolist. at(i))<<endl;
if(qvofile.is_o pen())
{
getline(qvofile ,line); // read dimensions dummy var
qvofile>>Nverti ces>>NFaces>>NE dges;
_vertex tmp;
for(int j =0; j<Nvertices; j++){
qvofile>>tmp.x> >tmp.y>>tmp.z ;
nodes.push_back (tmp);
}
qvofile.close() ;
}
else cout<<"unable to open qvo file"<<(qvolist .at(i)).c_str() <<endl;
}
// print list of vertices
for_each(nodes. begin(), nodes.end(),pri nt);

//Sort vertices by x co-ordinate
sort(nodes.begi n(), nodes.end(),sor tbyx);<-----------segmentation fault here

=============== =============== =============== =============

[tavianator]

The problem with your code is almost certainly with the part concerned with reading data from the file (or its a compiler bug). Without a definition for Read_qvofile_li st, I can't tell if it's in there or not. I did notice, however, that you make no check for end-of-file in your for loop; that is bad practice, for if you opened a file that was too short, your program wouldn't behave as expected. This may be the source of your segfault; I have found that programs rarely segfault where the actual problem was.

As well, it is generally good C++ practice to have all data members private, and declare member functions to get and set them, not that this has any relavance to the segfault.