Find all substring's occurrences and locations
I'm writing a program to parse some data sav开发者_JAVA技巧ed as text files. What I am trying to do is find the location of every needle in a haystack. I already can read the file in and determine the number of occurrences, but I am looking to find the index also.
string str,sub; // str is string to search, sub is the substring to search for
vector<size_t> positions; // holds all the positions that sub occurs within str
size_t pos = str.find(sub, 0);
while(pos != string::npos)
{
positions.push_back(pos);
pos = str.find(sub,pos+1);
}
Edit I misread your post, you said substring, and I assumed you meant you were searching a string. This will still work if you read the file into a string.
I know an answer has been accepted, but this will also work, and will save you having to load in the file to a string..
#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;
int main(void)
{
const char foo[] = "foo";
const size_t s_len = sizeof(foo) - 1; // ignore \0
char block[s_len] = {0};
ifstream f_in(<some file>);
vector<size_t> f_pos;
while(f_in.good())
{
fill(block, block + s_len, 0); // pedantic I guess..
size_t cpos = f_in.tellg();
// Get block by block..
f_in.read(block, s_len);
if (equal(block, block + s_len, foo))
{
f_pos.push_back(cpos);
}
else
{
f_in.seekg(cpos + 1); // rewind
}
}
}
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