So what happened to std::make_pair<> in C++11 ?

Hey there. I just transferred a small project I was working on on my other computer to try to integrate a bit of C++11 in it for fun but the compiler complains about the make_pair<>() function:

system.cpp:39:66: erreur: no matching function for call to ‘make_pair(std::string&, bool)’

If I just remove the command line argument saying that I want to use the C++11 standard it stops complaining and the project builds and runs fine.

What am I missing ?

In the meantime I can just make my own make_pair() function since it is rather straightforward, but I would rather just use the existing one of course.

Sorry, forgot the code.

Code:

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void FSMachine::SetState(std::string state, std::string& value) {
    states[state] = std::make_pair<std::string, bool>(value, true);
}

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Code:

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class FSMachine {
private:
    std::map<std::string, std::pair<std::string, bool> > states;
public:
    FSMachine();

    bool IsStateSet(std::string);
    void SetState(std::string, std::string& value);
    std::string ReadState(std::string);
};

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Did you #include <utility>?

Yes I did. I will try a clean + rebuild just in case.

Nope.

Code:

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"/usr/bin/make" -f nbproject/Makefile-Debug.mk QMAKE= SUBPROJECTS= .clean-conf
make[1]: entrant dans le répertoire « /cygdrive/c/Users/win7/Documents/NetBeansProjects/CppApplication_1 »
rm -f -r build/Debug
rm -f dist/Debug/Cygwin_4.x-Windows/cppapplication_1.exe
make[1]: quittant le répertoire « /cygdrive/c/Users/win7/Documents/NetBeansProjects/CppApplication_1 »

CLEAN SUCCESSFUL (total time: 1s)
"/usr/bin/make" -f nbproject/Makefile-Debug.mk QMAKE= SUBPROJECTS= .build-conf
make[1]: entrant dans le répertoire « /cygdrive/c/Users/win7/Documents/NetBeansProjects/CppApplication_1 »
"/usr/bin/make"  -f nbproject/Makefile-Debug.mk dist/Debug/Cygwin_4.x-Windows/cppapplication_1.exe
make[2]: entrant dans le répertoire « /cygdrive/c/Users/win7/Documents/NetBeansProjects/CppApplication_1 »
mkdir -p build/Debug/Cygwin_4.x-Windows
rm -f build/Debug/Cygwin_4.x-Windows/system.o.d
g++-4.exe -std=c++0x -Wall -Wextra  -c -g -MMD -MP -MF build/Debug/Cygwin_4.x-Windows/system.o.d -o build/Debug/Cygwin_4.x-Windows/system.o system.cpp
make[2]: quittant le répertoire « /cygdrive/c/Users/win7/Documents/NetBeansProjects/CppApplication_1 »
make[1]: quittant le répertoire « /cygdrive/c/Users/win7/Documents/NetBeansProjects/CppApplication_1 »
system.cpp: In member function ‘void FSMachine::SetState(std::string, std::string&)’:
system.cpp:39:66: erreur: no matching function for call to ‘make_pair(std::string&, bool)’
system.cpp: At global scope:
system.cpp:62:10: attention : unused parameter ‘msg’
make[2]: *** [build/Debug/Cygwin_4.x-Windows/system.o] Erreur 1
make[1]: *** [.build-conf] Erreur 2
make: *** [.build-impl] Erreur 2

BUILD FAILED (exit value 2, total time: 2s)

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Sorry, but I cannot reproduce your problem using g++ 4.4.5 with --std=c++0x.

Could it be a GCC bug ? I would normally never suspect the compiler being wrong, but since only removing the --std=c++0x argument fixes the problem I can't see why my code would be wrong :\

What version of g++ are you using?

How can I check that ? I tried to look for the version number but haven't found it. All I know is it's g++4 (but do not know what sub-version) and I have downloaded it yesterday from the Cygwin setup.exe.

When I compiled the code with g++ version 4.5.2 I got this error:

Quote:

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main.cpp||In member function ‘void FSMachine::SetState(std::string, std::string&)’:|
main.cpp|17|error: no matching function for call to ‘make_pair(std::string&, bool)’|
||=== Build finished: 1 errors, 0 warnings ===|

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I could get rid of the error by removing the --std=c++0x or by changing:

Code:

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void FSMachine::SetState(std::string state, std::string& value) {
    states[state] = std::make_pair<std::string, bool>(value, true);
}

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to

Code:

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void FSMachine::SetState(std::string state, std::string& value) {
    states[state] = std::make_pair<std::string&, bool>(value, true);
}

---

Quote:

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How can I check that ?

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Try g++ --version at the command line.

Jim

Aw thank you ! I'm using version 4.5.3 and changing to a reference seems to have solved the compiler error. I don't really get why it should be a reference though :\

Quote:

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Originally Posted by Alexandre

changing to a reference seems to have solved the compiler error. I don't really get why it should be a reference though

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Out of curiosity, but have you tried:

Code:

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states[state] = std::pair<std::string, bool>(value, true);

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Normally, I would expect make_pair to be used as:

Code:

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states[state] = std::make_pair(value, true);

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That is, the main point of make_pair is to be less verbose in having to specify the types explicitly.

Yes I have tried std::pair<> but it didn't work. I wish I could reproduce it for you but I am having a little issue with my IDE right now :/

Quote:

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Normally, I would expect make_pair to be used as:

Code:

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states[state] = std::make_pair(value, true);

---

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That does compile without errors for me and it looks like the better solution.

Jim

That does look like what I will switch to as soon as I fix my IDE. Thanks everyone.

IMHO the whole point of make_pair is that you don't have to specify the template parameters. Otherwise you might as well use this which as it happens is 5 characters shorter anyway:

Code:

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std::pair<std::string, bool>(value, true);

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So yes absolutely just omit the template arguments as suggested:

Code:

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std::make_pair(value, true);

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Edit: Hmm I seem to have just repeated what Laserlight said. I guess I should have read every response first, darn it. Oh well QFE.