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Asked: 2026-05-11T22:14:27+00:00

I’m trying to convert std::string to float/double . I tried: std::string num = 0.6;

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I’m trying to convert std::string to float/double.
I tried:

std::string num = "0.6";
double temp = (double)atof(num.c_str());

But it always returns zero. Any other ways?

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1 Answer

  1. Editorial Team
    std::string num = "0.6";
double temp = ::atof(num.c_str());

    Does it for me, it is a valid C++ syntax to convert a string to a double.

    You can do it with the stringstream or boost::lexical_cast but those come with a performance penalty.

    Ahaha you have a Qt project …

    QString winOpacity("0.6");
double temp = winOpacity.toDouble();

    Extra note:
    If the input data is a const char*, QByteArray::toDouble will be faster.

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