Member Avatar for ahspats

so my program has to read data from text file and pass it to the function. text file contains integer and string in every line. it looks like this:

23456 john
96512 martin
56985 wendy

i've written it in C using this code:

while (fscanf(filestream, "%d%s", &key, &value) == 2){
    Insert(key, value);
}

it would be very helpful if someone could write the exact equivalent in C++ for the given code.

Thank you in advance.

Edited by Reverend Jim because: Fixed formatting
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Dani AI

Generated

A compact, idiomatic C++ way to handle your file is to read it line-by-line, parse the integer key, then take the remainder of the line as the name (so multi-word names work). That also explains why saw only the first line: the program did one extraction and never repeated it in a loop. As and pointed out, using line-oriented input plus a stringstream makes parsing both simple and robust.

Here is a safe pattern that preserves spaces in names and skips malformed lines:

#include <fstream>
#include <sstream>
#include <string>

std::ifstream in("data.txt");
if (!in) { /* handle open error */ }

std::string line;
while (std::getline(in, line)) {
    if (line.empty()) continue;
    std::istringstream iss(line);
    int key;
    if (!(iss >> key)) continue;               // bad line: no integer
    std::string name;
    std::getline(iss >> std::ws, name);        // rest of line as name (preserve spaces)
    if (name.empty()) continue;                // bad line: no name
    d->insert(key, name);
}

Practical notes: always check that the file opened successfully; skip blank or malformed lines rather than crashing; using iss >> key avoids exceptions that std::stoi can throw; the iss >> std::ws call eats any spacing before the name. If your names will never contain spaces you can use simple token extraction in a loop for slightly simpler code, but the line+stringstream approach is safer and easier to validate.

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Member Avatar for Topi Ojala

Don't think anyone will write the code for you, too bad I don't really know C to begin with.

I bet you can find very similiar threads in the C++ forum history. If not, you should check getline, << and maybe string2int

Member Avatar for csurfer

Here is an algorithm for it :

//open a file using fstream objects say file and functions like file.open() in input mode
// Create a string variable which can act as a buffer for holding the values
while(getline( <file descriptor value>, <buffer object>)!=NULL)
{
int key;
string skey,value;
//extract string value of key into skey and convert it into integer using istringstream
//extract string value of key into value
//With the help of a new fstream object write into the file you want it to.
//erase the buffer for providing space for next input using file.erase() function
}
Member Avatar for ahspats

so i've got a bit further. i would've never believed that something like this can work, but it passes the right values. the problem is that it reads only the first line. here's the updated code:

file >> key;
file >> value;
d->insert(key, value);

how can i read the lines following the first one???

Member Avatar for csurfer

Well use getline function. It advances the file get pointer to next line automatically.Or even you can look upon f.seekg() function.

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