Member Avatar for B.Y

I have a s1.txt like this :

3,R,G,T
1,E
9,T,U,Y,O

Now I want to read each character of a each line ...do some analysis and then read each character of the next line ...do some analysis ...so on till EOF.

How do I go abt this?

Well ...I jus wrote a simple program to read a file as below:

#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;
int main() {
    //char sum = 0;
    char x;
    ifstream inFile("s1.txt");
    if (!inFile) {
        cout << "Unable to open file";
        exit(1);
    }
    while (x != '\n') {
    while (inFile >> x) {    
       
        cout<<"x = "<<x<<endl;
        
    }
    }
    inFile.close();
   
    getchar();
    return 0;
}

Doing the above ...I get the entire file as output ... why is'nt it stopping execution as soon as it hits a newline as I mentioned in the first while loop? After I get the first line ...how do I parse through it to analyse each character in the line?

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  • 4 Replies
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  • 19 Hours Discussion Span
  • Latest Post Latest Post by WaltP

Dani AI

Generated

Two separate issues make your loop never stop at newlines: (1) x is uninitialized when you first test it, which is undefined behavior, and (2) formatted extraction with operator>> on char skips whitespace by default, so it never returns '\n'. To see every character (including newlines), use unformatted input like istream::get, or turn off skipping of whitespace. See istream::get and std::noskipws.

Character-by-character, keeping track of line boundaries:

std::ifstream in("s1.txt");
char ch;
std::size_t line_no = 1;
while (in.get(ch)) {
    if (ch == '\r') continue;      // handle CRLF on Windows
    if (ch == '\n') { ++line_no; continue; }
    // analyze ch on line_no
}

If you prefer line-by-line, std::getline reads a full line (without the trailing newline). You can then split on commas and inspect characters, skipping spaces safely:

std::ifstream in("s1.txt");
std::string line;
for (std::size_t line_no = 1; std::getline(in, line); ++line_no) {
    std::istringstream ss(line);
    std::string field;
    while (std::getline(ss, field, ',')) {
        for (unsigned char c : field) {
            if (std::isspace(c)) continue;  // cast to unsigned char for ctype
            // analyze c from this field on line_no
        }
    }
}

Avoid strtok here; it requires mutable C strings and is not idiomatic C++. Refer to std::getline and std::isspace for details.

Recommended Answers

All 4 Replies

Member Avatar for rati

You can use strtok function using string.h
It helps u to get the string tokens based on the delimiter u give.

Member Avatar for thekashyap

You know there is also www.google.com where you can search for words like "C++ split line"
or "C++ tokens"...
Or use RWCTokenizer..

Member Avatar for vijayan121

a. read one line
b. strip off unwanted chars (non-printable/whitespace/,)
c. analyze the remaining chars.
repeat a,b,c till end of file.

struct is_2b_thrown_away
{
  bool operator() ( char ch ) const
  { return !isprint(ch) || isspace(ch) || (ch==',') ; }
};

void process_file( const char* file_name )
{
    ifstream file(file_name) ;
    string line ;
    while( getline( file, line ) )
    {
       vector<char> chars ;
       remove_copy_if( line.begin(), line.end(), back_inserter(chars), 
                                      is_2b_thrown_away() ) ;
       // analyse characters in vector chars
    }
}
Member Avatar for WaltP

Mostly what vijayan121 suggests
a. read one line
b. analyze each character
c. do what you need with each character
repeat a,b,c till end of file.

string line ;
while( getline( file, line ) )
{
    for (i=0; i < line.length(); i++)
    {
         if (line[i] ...)    // look at each character and process it accordingly
    }
}
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