Search through a file for a string
 

Hi,

I'm very new to C++ and was wondering how I would go about searching for a string (AT+COPS?) in a file and displaying everything to the right of the string, could someone point me in the direction of a guide

cheers

Re: Search through a file for a string
 

Open the file read it line by line as a string and then use a string api to search for the keyword. It is quite cumbersome homework I would say.

Re: Search through a file for a string
 

The hardest part is opening the file, then it's just like reading input from cin:

#include <fstream>

#include <iostream>

#include <string>



int main()

{

  std::ifstream is("myfile");

  std::string line;



  while (std::getline(is, line)) {

    std::string::size_type start = line.find("AT+COPS");



    if (start != std::string::npos)

      std::cout << line.substr(start) << '\n';

  }

}

Re: Search through a file for a string
 

to assignt the output to a varaible would I do something like

String copsoutput;
copsoutput = line.substr(start);

I'm more of a visual baic & c# man, and wish my project would let write it in VB or C#
cheers

Re: Search through a file for a string
 

>> I'm more of a visual baic & c# man, and wish my project would let write it in VB or C#
This is c++ board. If you want vb or c# then ask your question there.

>>String copsoutput;
That needs to be lower-case s on string

string copsoutput;

>>to assignt the output to a varaible would I do something like
Yes -- you got the idea :)

Re: Search through a file for a string
 

lucky I'm trying to write a c++ program then ;)
anyhow when i try to complie the app using

while (std::getline(is, line)) 

                        {

                        std::string::size_type start = line.find("+COPS:");

                        if (start != std::string::npos)

                        write(lcd,secondrow,sizeof(secondrow));

                        copsoutput = line.substr(start);

                        write(lcd,copsoutput,sizeof(copsoutput));

                        }

I receive the following error:

cannot convert std::string to const void for argument 2 to ssize_t write(int, const void*, size_t)

Re: Search through a file for a string
 

>>cannot convert std::string to const void for argument 2 to ssize_t write(int, const void*, size_t)

the function write is wanting a pointer as the second parameter and you are passing std::string. The third parameter is also wrong. try this:

write(lcd,copsoutput.c_str(), copsoutput.length());

Re: Search through a file for a string
 

now the app compiles but when I run it I thrown out with

terminate called after throwing an instance of 'std::out_of_range'

  what():  basic_string::substr

Aborted

Re: Search through a file for a string
 

what is secondrow ?

while (std::getline(is, line)) 

{

    std::string::size_type start = line.find("+COPS:");

    if (start != std::string::npos)

    {

         write(lcd,secondrow,sizeof(secondrow));

         copsoutput = line.substr(start);

         write(lcd,copsoutput.c_str(), copsoutput.length());

    }

}