Reputation: 41
I cannot work out how to read text from a file rather than from getchar()
calc entropy of a string
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include <string>
#include <iostream>
#include <cmath>
#include <fstream>
#include <cstring>
using namespace std;
double log2(double number)
{
return log(number)/std::log(2.);
}
int main() {
unsigned long table[256], total = 0;
double entropy = 0;
char mychar;
string line;
ifstream myfile ("sometext.txt");
if (myfile.is_open())
{
while ( getline (myfile,line) )
{
cout << line << '\n';
}
}
short i;
for(i=0; i<256; i++)
table[i] = 0;
while(1)
{
mychar = getchar();
how to read from myfile.txt ?
if (mychar==EOF) // ctrl Z
{break;}
table[mychar]++;
}
for(i=33;i<127;i++)
if(table[i]) {
total += table[i];
entropy -= log2(table[i])*table[i];
}
entropy /= total;
entropy += log2(total);
printf("Total Characters: %6d\n",total);
printf("Entropy: %5.6f\n",entropy);
}
Upvotes: 0
Views: 461
Reputation: 154045
The loop reading lines with std::getline()
reads the content of the file! You could actually process the data from the std::string
s already read:
while (std::getline(myfile, line)) {
std::cout << line << '\n';
for (std::string::const_iterator it(line.begin()), end(line.end()); it != end; ++it) {
unsigned char mychar = *it;
++table[mychar];
}
}
The inner loop iterates over all characters in the string line
. It obtains an unsigned char
from the character currently processed (i.e., from *it
) because char
may be signed type and yield negative values which probably doesn't work too well. The ASCII characters are all positive but, e.g., the u-umlaut ü
from my name may become a negative values; I'd guess that isn't really an issue for your input but I prefer code which works even when unexpected things happen.
In any case, this loops terminates when the std::getline()
failed because there is no further data. If you want to read the data again, you'll either need to open a new std::ifstream
or reset the std::ifstream
you got:
myfile.clear(); // clear error flags
myfile.seekg(0, std::ios_base::beg); // move to the start of the file
To actually read individual chars as int
you could use
mychar = myfile.get();
Personally, I'd be inclined to read the characters using iterators, though:
for (std::istreambuf_iterator<char> it(myfile), end; it != end; ++it) {
char mychar = *it; // well, you could keep using *it, of course
// ...
}
Upvotes: 2