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Juan Pinzón
Asked: 2020-11-02 12:40:49 +0800 CST 2020-11-02 12:40:49 +0800 CST

Concatenate a string with a float C++

  • 772

I have a problem concatenating a string variable with a float, I have the following:

float c1 = 0, c2 = 0, c3 = 0;
std::string best = "";

Then I use it as follows:

best = "Imagen 1: " + c1;
best = "Imagen 2: " + c2;
best = "Imagen 3: " + c3;

However, it gives me the following errors:

../src/Test.cpp:91:24: error: invalid operands of types ‘const char [11]’ and ‘float’ to binary ‘operator+’
    best = "Imagen 1: "+c1;
                        ^
../src/Test.cpp:93:24: error: invalid operands of types ‘const char [11]’ and ‘float’ to binary ‘operator+’
    best = "Imagen 2: "+c2;
                        ^
../src/Test.cpp:95:24: error: invalid operands of types ‘const char [11]’ and ‘float’ to binary ‘operator+’
    best = "Imagen 3: "+c3;

How could I fix it?

c++

2 Answers

  1. Best Answer

    In C++11, you can use the method to_stringlike this:

    best = "Imagen 1: " + std::to_string(c1);
best = "Imagen 2: " + std::to_string(c2);
best = "Imagen 3: " + std::to_string(c3);

    Before C++11, it could be done with stringstream:

    #include <sstream>

std::stringstream ss;

ss << "Imagen 1: " << std::to_string(c1);
best = ss.str();

ss.str(std::string());

ss << "Imagen 1: " << std::to_string(c2);
best = ss.str();

ss.str(std::string());

ss << "Imagen 1: " << std::to_string(c3);
best = ss.str();

ss.str(std::string());

    Or better as @Peregring-lk said, you can create a method to do it however you want:

    #include <sstream>

std::string floatToString(const float& val) {
    std::stringstream ss;
    ss << val;
    return ss.str();
} 

best = "Imagen 1: " + floatToString(c1);
best = "Imagen 2: " + floatToString(c2);
best = "Imagen 3: " + floatToString(c3);
    • 2 
  2. #include <sstream>

std::ostringstream oss;
oss << c1;
best = "Imagen 1" + c1.str();

    And so for each conversion you want to do. It is best to create your own method:

    #include <sstream>

std::string f2string(const float& val)
{
    std::ostringstream os;

    os << val;

    return os.str();
}

best = "Imagen 1" + f2string(c1);
best = "Imagen 2" + f2string(c2);
best = "Imagen 3" + f2string(c3);
    • 2