CODEWITHSUNDEEP
c++
Dean
Dean

Reputation: 517

how to cast char * as doubles?

i have a struct with x,y,z as the type double. I'm trying to split the lines by spaces and then put the values of that array into my structure but it fails to work, can someone tell me what to do?

#include "_externals.h"
#include <vector>

typedef struct
{
    double X, Y, Z;
} p;

p vert = { 0.0, 0.0, 0.0 };

int main()
{
    char *path = "C:\\data.poi";    

    ifstream inf(path);
    ifstream::pos_type size;
    inf.seekg(0, inf.end);
    size = inf.tellg();

    double x, y, z;
    char *data;

    data = new char[size];
    inf.seekg(inf.beg);
    inf.read(data, size);
    inf.seekg(inf.beg);

    char** p = &data;
    char *line = *p;    

    for (int i = 0; i < strlen(data); ++i)
    {
        const char *verts = strtok(line, " ");

        //this isnt working
        vert.X = verts[0];
        vert.Y = verts[1];
        vert.Z = verts[2];

        ++*line;
    }

}

thanks

Upvotes: 1

Views: 205

Answers (2)

johnsyweb
johnsyweb

Reputation: 141770

You cannot (meaningfully) cast a char* as a double, but you can extract from a stream into a double.

Since you are splitting the input line on spaces, the typical idiom is like this... for each line in the file, create an istringstream object and use this to populate your structure.

If operator >>() fails (e.g. if a letter was entered where a digit is expected) the target value is left unmodified and failbit is set.

For example:

#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>

struct coords
{
    double X, Y, Z;
};


int main()
{
    std::ifstream inf("data.poi");
    std::vector<coords> verts;
    std::string line;
    while (std::getline(inf, line))
    {
        std::istringstream iss(line);
        coords coord;

        if (iss >> coord.X >> coord.Y >> coord.Z)
        {
            verts.push_back(coord);
        }
        else
        {
            std::cerr << "Could not process " << line << std::endl;
        }
    }
}

Upvotes: 6

Erwald
Erwald

Reputation: 2206

The same way you would do it for an integer with atoi.

For conversion from char* to double, simply use :

atof

atof example .

Upvotes: 0

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