Trying to understand how to use the auto keyword correctly
Guys/Gals, i am a definite n00b. i started trying to learn C++ as my first language about 3 days ago. Please be gentle with me lol. Having said that, I have a book that tries to explain how to use the auto keyword but the code in the lesson fails to compile both in Linux (using GCC compiler and in MS Visual C++ Studio.) Searching for an answer has brought me here. The decltype function is what i think i am missing. i will look that up but i want to be pointed in the right direction. the code in the lesson is...
//Pre-Processor Directive
#include <iostream>
//Declaring namespace type
using namespace std;
int main ( )
{
auto Flag = true;
auto Number = 2500000000000;
cout << "Flag = " << Flag;
cout << ", sizeof(Flag) = " << sizeof(Flag) << endl;
cout << "Number = " << Number;
cout << " , sizeof(Number) = " << sizeof(Number) << endl;
return 0;
}
and the fail message i get is ..
moses@linux-8sfs:~/C++_Lessons/cpp> g++ -o online3.5 online3.5.cpp
online3.5.cpp: In function ‘int main()’:
online3.5.cpp:6:10: error: ‘Flag’ does not name a type
online3.5.cpp:7:10: error: ‘Number’ does not name a type
online3.5.cpp:9:26: error: ‘Flag’ was not declared in this scope
online3.5.cpp:11:28: error: ‘Number’ was not declared in this scope
please ignore the //comments. they are mine. It seems the compiler is looking for a type declaration (or i have done something that makes my auto irrelevant). if anyone could just point me in the right direction, i will do the work. thanks in advance -- the Diesel
@giblit
Do you have c++11 turned on? Check your compiler settings.
yes i will check that . i thought that was automatic on the MS Studio version though. i will let you know
btw why are you trying to.get the size of a boolean
it's just an excercise in a teach-yourself book. i try not to skip ahead but my guess is the author is trying to teach memory management as well as variables and constants.
//Pre-Processor Directive
#include <iostream>
//Declaring namespace type
using namespace std;
int main ( )
{
auto Flag = true;
auto Number = 2500000000000;
cout << "Flag = " << Flag;
cout << ", sizeof(Flag) = " << sizeof(Flag) << endl;
cout << "Number = " << Number;
cout << " , sizeof(Number) = " << sizeof(Number) << endl;
return 0;
}
and the fail message i get is ..
moses@linux-8sfs:~/C++_Lessons/cpp> g++ -o online3.5 online3.5.cpp
online3.5.cpp: In function ‘int main()’:
online3.5.cpp:6:10: error: ‘Flag’ does not name a type
online3.5.cpp:7:10: error: ‘Number’ does not name a type
online3.5.cpp:9:26: error: ‘Flag’ was not declared in this scope
online3.5.cpp:11:28: error: ‘Number’ was not declared in this scope
please ignore the //comments. they are mine. It seems the compiler is looking for a type declaration (or i have done something that makes my auto irrelevant). if anyone could just point me in the right direction, i will do the work. thanks in advance -- the Diesel
@giblit
Do you have c++11 turned on? Check your compiler settings.
yes i will check that . i thought that was automatic on the MS Studio version though. i will let you know
btw why are you trying to.get the size of a boolean
it's just an excercise in a teach-yourself book. i try not to skip ahead but my guess is the author is trying to teach memory management as well as variables and constants.
Last edited on
Your code is valid.
From the error I can dedude that compiler thinks of auto in this case as of storage duration specifier, so you really does not have C++11 mode turned on.
From the error I can dedude that compiler thinks of auto in this case as of storage duration specifier, so you really does not have C++11 mode turned on.
| i thought that was automatic on the MS Studio version though. i will let you know |
moses@linux-8sfs:~/C++_Lessons/cpp> g++ -o online3.5 online3.5.cpp |
Say what?
Last edited on
| # g++ -o online3.5 online3.5.cpp |
g++ (GCC), even the latest version, does default to the older standard. Add "-std=c++11" option and preferably "-Wall" too.
man g++The C++ compiler of MS Visual Studio on the other hand does default to most of what it can. However, only the latest VS 2012 supports significant amount of C++11. Speaking of MS defaults, the default at least in Express is to still compile 32-bit binaries (but luckily the compiler can produce 64-bit code too.)
Last edited on
@MiiNiPaa thanks for the confirmation!!!!
@cire lol. i think you are laughing at the fact that i am pasting output from a GCC compiler and saying that it errored out in VS studio. i was just trying to show the error (as it was essentially the same on both compilers.) If not, i will read this again in a month or so and realize that there is only a very thin line between n00b-ness and idiocy (sometimes i cross over it).
@keskiverto thank you i will read the man pages and add those options. i appreciate the help.
@cire lol. i think you are laughing at the fact that i am pasting output from a GCC compiler and saying that it errored out in VS studio. i was just trying to show the error (as it was essentially the same on both compilers.) If not, i will read this again in a month or so and realize that there is only a very thin line between n00b-ness and idiocy (sometimes i cross over it).
@keskiverto thank you i will read the man pages and add those options. i appreciate the help.
Topic archived. No new replies allowed.