Passing a object member to a template function expecting an integer

Question

I have been reading and reading posts asking similar questions but my doubts persists.

So I have a class like this:

class Instruction{
public:
    unsigned int getAddress();
    uint32_t getValue();
private:
    unsigned int address;
    uint32_t value;
}

Then I need to convert a decimal to hexadecimal an write it to a string. I saw this question so I took the function in the answer and put it my Utils.hpp class like this:

Utils.hpp

class Utils{
public:
    ...
    static template< typename T > static std::string toHex( T &i );
}

Utils.cpp

template< typename T >
std::string toHex( T &i ){
    std::stringstream stream;
    stream  << "0x" << std::setfill ('0') << std::setw(sizeof(T)*2)
            << std::hex << i;
    return stream.str();
}
std::string Utils::toHex<unsigned int>();
std::string Utils::toHex<uint32_t>();

On main I have this:

std::stringstream stream;

Instruction *newInstruction = new Instruction(addr, inst); // this attributes the parameters

stream  << Utils::toHex(newInstruction->getAddress()) << " "
        << Utils::toHex(newInstruction->getValue()) << endl;

And I get the following compiling errors:

main.cpp: In function 'int main(int, char**)':
main.cpp:39: error: no matching function for call to 'Utils::toHex(unsigned int)'
Utils.hpp:16: note: candidates are: static std::string Utils::toHex(T&) [with T = unsigned int]
main.cpp:41: error: no matching function for call to Utils::toHex(uint32_t)'
Utils.hpp:16: note: candidates are: static std::string Utils::toHex(T&) [with T = unsigned int]
make: *** [main.o] Error 1

I really need help to figure out how I can make this work, because I am relatively new to this stuff.

Thank you in advance!

Which posts did you read? All the ones I remember on the topic give the same answer! — Lightness Races in Orbit, Jul 09 '15 at 13:40

score 4 · Accepted Answer · edited Jul 09 '15 at 13:42

4

You should make toHex accept const reference to T: toHex(const T&). Otherwise you cannot pass a temporary to it, whereas the result of function call is a temporary.

Also note that the question/answer you are referring to is not working with references at all, it has

std::string int_to_hex( T i )

edited Jul 09 '15 at 13:42

Barry

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answered Jul 09 '15 at 13:39

Petr

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score 1 · Answer 2 · answered Jul 09 '15 at 13:43

You are missing Utils:: prefix in the definition of the function and, as said earlier, const in the reference. The corrected Utils.cpp should be:

template< typename T >
std::string Utils::toHex(const T &i ){
    std::stringstream stream;
    stream  << "0x" << std::setfill ('0') << std::setw(sizeof(T)*2)
            << std::hex << i;
    return stream.str();
}

Passing a object member to a template function expecting an integer

2 Answers2