Question

I’m a beginner to C++, so please be understanding…

I want to search for a string (needle) within a file (haystack), by reading each line separately, then searching for the needle in that line. However, ideally for a more robust code I would like to be able to just read individual words on the line, so that if there are larger (i.e. multiple) white-space gaps betweeen words they are ignored when searching for the needle. (e.g perhaps using the >> operator??) That is, the needle string should not have to exactly match the size of the space between words in the file.

so for example, if I have a needle:

"The quick brown fox jumps over the lazy dog" 

in the file this might be written (on a particular line) as:

... "The quick brown      fox jumps over the        lazy dog" ...

Is there an efficient way to do this?

Currently I include the necessary number of spaces in my needle string but I would like to improve the code, if possible.

My code currently looks something like the following (within a method in a class):

double var1, var2;
char skip[5];
std::fstream haystack ("filename");
std::string needle = "This is a string, and var1    =";
std::string line;
int pos;
bool found = false;

// Search for needle
while ( !found && getline (haystack,line) ) {
  pos = line.find(needle);  // find position of needle in current line

  if (pos != std::string::npos) { // current line contains needle

      std::stringstream lineStream(line);
      lineStream.seekg (pos + needle.length());
      lineStream >> var1;
      lineStream >> skip;
      lineStream >> var2;
      found = true;
  }
}

(Just for clarity, after finding the string (needle) I want to store the next word on that line or in some cases store the next word, then skip a word and store the following word, for example:

With a file:

... ...
... This is a string, and var1    = 111 and 777 ...
... ...

I want to extract var1 = 111; var2 = 777; )

Thanks in advance for any help!

Answer 1

This will work, although I think there’s a shorter solution:

std::size_t myfind(std::string ins, std::string str) {
  for(std::string::iterator it = ins.begin(), mi = str.begin(); it != ins.end(); ++it) {
    if(*it == *mi) {
      ++mi;
      if (mi == str.end())
        return std::distance(ins.begin(),it);
    }
    else {
      if(*it == ' ')
        continue;
      mi = str.begin();
    }
  }
  return std::string::npos;
}
// use:
myfind("foo The quick brown      fox jumps over the        lazy dog bar", "The quick brown fox");