Trouble with C++ file I/O - c++

Question

Noobie Alert.
Ugh. I'm having some real trouble getting some basic file I/O stuff done using <stdio.h> or <fstream>. They both seem so clunky and non-intuitive to use. I mean, why couldn't C++ just provide a way to get a char* pointer to the first char in the file? That's all I'd ever want.
I'm doing Project Euler Question 13 and need to play with 50-digit numbers. I have the 150 numbers stored in the file 13.txt and I'm trying to create a 150x50 array so I can play with the digits of each number directly. But I'm having tons of trouble. I've tried using the C++ <fstream> library and recently straight <stdio.h> to get it done, but something must not be clicking for me. Here's what I have;
#include <iostream>
#include <stdio.h>
int main() {
const unsigned N = 100;
const unsigned D = 50;
unsigned short nums[N][D];
FILE* f = fopen("13.txt", "r");
//error-checking for NULL return
unsigned short *d_ptr = &nums[0][0];
int c = 0;
while ((c = fgetc(f)) != EOF) {
if (c == '\n' || c == '\t' || c == ' ') {
continue;
}
*d_ptr = (short)(c-0x30);
++d_ptr;
}
fclose(f);
//do stuff
return 0;
}
Can someone offer some advice? Perhaps a C++ guy on which I/O library they prefer?

Answer 1

Here's a nice efficient solution (but doesn't work with pipes):
std::vector<char> content;
FILE* f = fopen("13.txt", "r");
// error-checking goes here
fseek(f, 0, SEEK_END);
content.resize(ftell(f));
fseek(f, 0, SEEK_BEGIN);
fread(&content[0], 1, content.size(), f);
fclose(f);
Here's another:
std::vector<char> content;
struct stat fileinfo;
stat("13.txt", &fileinfo);
// error-checking goes here
content.resize(fileinfo.st_size);
FILE* f = fopen("13.txt", "r");
// error-checking goes here
fread(&content[0], 1, content.size(), f);
// error-checking goes here
fclose(f);

Answer 2

I would use an fstream. The one problem you have is that you obviously can't fit the numbers in the file into any of C++'s native numeric types (double, long long, etc.)
Reading them into strings is pretty easy though:
std::fstream in("13.txt");
std::vector<std::string> numbers((std::istream_iterator<std::string>(in)),
std::istream_iterator<std::string>());
That will read in each number into a string, so the number that was on the first line will be in numbers[0], the second line in numbers[1], and so on.
If you really want to do the job in C, it can still be quite a lot easier than what you have above:
char *dupe(char const *in) {
char *ret;
if (NULL != (ret=malloc(strlen(in)+1))
strcpy(ret, in);
return ret;
}
// read the data:
char buffer[256];
char *strings[256];
size_t pos = 0;
while (fgets(buffer, sizeof(buffer), stdin)
strings[pos++] = dupe(buffer);

Answer 3

Rather than reading the one hundred 50 digit numbers from a file, why not read them directly in from a character constant?
You could start your code out with:
static const char numbers[] =
"37107287533902102798797998220837590246510135740250"
"46376937677490009712648124896970078050417018260538"...
With a semicolon at the last line.