Read complex numbers (a+bi) from text file in C++

Question

i want to read an array of complex numbers (in a+bi form). There are several suggestions I found on the internet, however those methods only result the real part , while the imaginary part is always 0 . And infact the real part of the next number is the imaginary of the previous number.

For example, I have an text file as follow:

2+4i
1+5i
7+6i

And here is a suggestion for reading complex data

int nRow = 3;
std::complex<int> c;
std::ifstream fin("test.txt");
std::string line;
std::vector<std::complex<int> > vec;
vec.reserve(nRow);
while (std::getline(fin, line))
{
    std::stringstream stream(line);
    while (stream >> c)
    {
        vec.push_back(c);
    }
}

for (int i = 0; i < nRow; i++){
    cout << vec[i].real() << "\t" << vec[i].imag() << endl;
}

while (1);
return 0;

And the output result is:

2   0
4   0
1   0

Is there a proper way to read a+bi complex numbers from text file? Or do I have to read the data as a string, and then process the string to extract and convert it back to complex numer?

Thanks !

Answer 1

One option is to read separately the real and imaginary part in 2 int s, and the sign into a char , then emplace_back into the complex vector, like

int re, im;
char sign;
while (stream >> re >> sign >> im)
{
    vec.emplace_back(re, (sign == '-') ? -im : im);
}

Here sign is a char variable that "eats" up the sign.

Answer 2

FILE *fp;
char line[80];
int a, b;

if ((fp = fopen("filename", "r") != NULL)
    while (fgets(line, 80, fp) != NULL) {
        if (sscanf(line, "%d + %di", &a, &b) == 2)
            /* do something with a and b */
        else
            fprintf(stderr, "Not in a+bi form");
    }

Answer 3

Your requirement (the format of input you seek) does not correspond to the method you are using to read it. The default streaming of a complex is the real and the imaginary part separated by spaces and in brackets - the sign between is not mandatory, and the trailing i is not required.

The obvious way to parse for input you seek is to read the real part, read a character, check if the character is a signed ( + or - ) and ignore spaces, then read the imaginary part. That is trivial with istream s.

Answer 4

int real[10] = { 0 };
int imaginary[10] = { 0 };
FILE *lpFile = fopen("filename" "rt"); // Open the file
for (int i = 0; i < 10; i++) {
    fscanf(lpFile, "%d+%di", &real[i], &imaginary[i]); // Read data 10 times
}
fclose(lpFile); // Close the file

This example code will read 10 complex numbers from a file.