populating char** - c++

Question

I'm trying to read in a list of files from another file. The file reading works but populating the array of char* isn't. It works for the first iteration but then gets a bad pointer on the next line. I tried with a vector of strings but was having problems, I think due to its destructor trying to free an argv.
char **datafiles = (char**)malloc(0);
int filecount = 0;
master.AddDataFiles(argv[1],datafiles,filecount);
int Manager::AddDataFiles(char *filename, char **filelist, int &filecount)
{
const int LINEMAX = 64;
struct stat info;
std::ifstream is(filename);
if (is.fail()) return 1;
char buffer[LINEMAX];
while(!is.eof())
{
is.getline(buffer,LINEMAX);
realloc(filelist,sizeof(char**) * (filecount + 1));
filelist[filecount] = (char*) malloc(std::strlen(buffer) + 1);
std::strcpy(filelist[filecount],buffer);
filecount++;
}
return 0;
}

Answer 1

Using realloc correctly is a bit tricky -- it can (and sometimes, but not always, will) return a different pointer than the one you passed to it, so you have to do something like this:
char **temp = realloc(filelist, sizeof(char**) * filecount+1);
if (temp != NULL)
filelist = temp;
else
failed_allocation();
Also note that your while (!file.eof()) is a classic mistake -- it won't sense the end of the file correctly.
I'd revisit the vector of strings option though. Perhaps you could post the code you had, and ask about whatever problem(s) you encountered with it. Getting it to work well will almost certainly be less work than fixing this, and the result will almost certainly be more solid and understandable.
Correct code for this would look something like:
std::vector<std::string> Manager::AddDataFiles(std::string const &filename) {
std::ifstream infile(filename.cstr());
std::vector<std::string> filenames;
std::string temp;
while (std::getline(infile, temp))
filenames.push_back(temp);
return filenames;
}

Answer 2

Why don't you use std::vector<std::string> instead of char**? This elegantly solves your problem!
If the filenames do not contain space then here is even more elegant solution (or else you can see Jerry's solution):
void Manager::AddDataFiles(const char *filename, std::vector<std::string> &filelist)
{
std::istream_iterator<string> start(std::ifstream(filename));
std::istream_iterator<string> end;
std::copy(start, end, std::back_inserter(filelist));
}
For this, you've to include these:
#include <iterator>
#include <algorithm>
#include <vector>
#include <string>

Answer 3

Use a std::string and std::vector<std::string>. It might also makes sense to have the file list a member.
#include <fstream>
#include <string>
#include <vector>
void Manager::AddDataFiles(const std::string& filename)
{
std::ifstream in(filename.c_str());
for( std::string line; std::getline(in, line); ) {
filelist.push_back(line);
}
}