I want to use c++11/14 features like range-based loops, but get a warning while doing g++ program.cpp. If done with compiler flag g++ -std=c++11 program.cpp the warning goes away. Is there a way to use c++11/14 by default on the g++ command (i.e without passing compiler flag every time).
Please explain to someone with limited knowledge of compilers and only need the c++11/14 features for competitive programming problems (even if it's a bad idea in general, maybe due to backward compatibility?)
Short Answer: Update your g++
According to g++ documentation
The default, if no C++ language dialect options are given, is -std=gnu++17.
You are probably using an older version of g++. You can check it using by running g++ --version in your terminal. If you are using Linux, you can also extract your default c++ standard from g++ manual with the command man g++ | col -b | grep -B 1 -e '-std.* default' in your terminal.
If you do not want to update your g++, you can also set a command alias by putting something like alias g+++='g++ -std=c++14' in your .bashrc
If you're using a gcc version > 4.9.3 use this command: g++ -std=c++14 program.cpp
If you're using an older version than that use g++ -std=c++1y program.cpp
Note: Consider adding the -Wall flag before program.cpp in your command to get warnings, they help you way more than you'd think!
Tip: If you're a starting developer and don't want too steep of a learning curve, try using an IDE before going full command-line.
EDIT: If you want a command to be "the default" you can add something like alias mycc='g++ -std=c++14 -Wall' in your .bashrc or .bash_profile file (see this link), then you'll be able to use mycc program.cpp
Related
I wanted to compile C++11 source code within Mac Terminal but failed. I tried g++ -std=c++11, g++ -std=c++0x, g++ -std=gnu++11 and g++ -std=gnu++0x but nothing worked. Terminal always read unrecognized command line option. However, g++ -std=gnu and things like that worked fine (of course C++11 source code could not pass).
Which option should I use to turn on C++11 support?
By the way, the command line tool I'm using is installed within Xcode, and I'm pretty sure that they are up-to-date.
As others have pointed out you should use clang++ rather than g++. Also, you should use the libc++ library instead of the default libstdc++; The included version of libstdc++ is quite old and therefore does not include C++11 library features.
clang++ -std=c++11 -stdlib=libc++ -Weverything main.cpp
If you haven't installed the command line tools for Xcode you can run the compiler and other tools without doing that by using the xcrun tool.
xcrun clang++ -std=c++11 -stdlib=libc++ -Weverything main.cpp
Also if there's a particular warning you want to disable you can pass additional flags to the compiler to do so. At the end of the warning messages it shows you the most specific flag that would enable the warning. To disable that warning you prepend no- to the warning name.
For example you probably don't want the c++98 compatibility warnings. At the end of those warnings it shows the flag -Wc++98-compat and to disable them you pass -Wno-c++98-compat.
XCode uses clang and clang++ when compiling, not g++ (assuming you haven't customized things). Instead, try:
$ cat t.cpp
#include <iostream>
int main()
{
int* p = nullptr;
std::cout << p << std::endl;
}
$ clang++ -std=c++11 -stdlib=libc++ t.cpp
$ ./a.out
0x0
Thanks to bames53's answer for pointing out that I had left out -stdlib=libc++.
If you want to use some GNU extensions (and also use C++11), you can use -std=gnu++11 instead of -std=c++11, which will turn on C++11 mode and also keep GNU extensions enabled.
Let's say we have a simple c++ file named hello.cpp which prints "Hello World!".
We generally create the executable using g++ hello.cpp. When I tried executing the command c++ hello.cpp it creates the executable successfully. Shouldn't it throw an error saying there is no c++ command available? and suggest us to use g++?
I tried running man c++ on the terminal, this brings up the GNU C Project page. So, does the terminal replace our c++ hello.cpp with g++ hello.cpp internally? It shouldn't do that right?
Additional Info:
Similarly, if I have a hello.c program that prints "Hello World!". When I execute c hello.c on the command line, I get the error:
$ c hello.c
c: command not found
This is expected since we have to use gcc hello.c. Why am not getting a similar error for the c++ hello.cpp?
On my Ubuntu system, I see this:
$ ls -l /usr/bin/c++
lrwxrwxrwx 1 root root 21 May 6 2019 /usr/bin/c++ -> /etc/alternatives/c++
$ ls -l /etc/alternatives/c++
lrwxrwxrwx 1 root root 12 May 6 2019 /etc/alternatives/c++ -> /usr/bin/g++
So c++ is actually an alias (symbolic link) to g++
The alternatives system allows changing what compiler c++ is an alias to:
$ update-alternatives --display c++
c++ - auto mode
link best version is /usr/bin/g++
link currently points to /usr/bin/g++
link c++ is /usr/bin/c++
slave c++.1.gz is /usr/share/man/man1/c++.1.gz
/usr/bin/clang++ - priority 10
/usr/bin/g++ - priority 20
slave c++.1.gz: /usr/share/man/man1/g++.1.gz
So c++ could actually be either g++ or clang++
For a C compiler, you don't want the c command, but cc, which again, could be either gcc or clang.
My CentOS system isn't quite so obvious with the symlinks, but g++ --version and c++ --version give the same output and both say they are g++. However, cc is a direct symlink to gcc there.
Shouldn't it throw an error saying there is no c++ command available? and suggest us to use g++?
Weeelll, there are no regulations or standards that restrict or require c++ command to do anything, so there is no "should" or "shouldn't". However, it would be strongly expected that c++ is a working C++ compatible compiler, that supports similar or same flags as cc does.
does the terminal replace our c++ hello.cpp with g++ hello.cpp internally?
A terminal is the device that displays things. Terminal does not replace it, it has no effect on it.
Most probably your system designer, but maybe administrator or publisher or distributor or package designer (or anyone in the chain), configured your system to provide a command named c++. Usually, that command is a symbolic link to a working C++ compiler, usually g++ on Linux systems. On my system, /usr/bin/c++ program is just installed with package named gcc, but some systems allow it to be configurable.
It shouldn't do that right?
As stated above, terminal shouldn't replace commands, it has no effect on it.
This is expected since
It is expected since there is no command named c. There are endless other unknown commands.
cc is the good old name for a C compiler. c99 is the standardized name of C99 compatible compiler.
Why am not getting a similar error for the c++ hello.cpp?
Because a command named c++ exists on your system.
I have recently started learning C++ and, since I'm on Linux, I'm compiling using G++.
Now, the tutorial I'm following says
If you happen to have a Linux or Mac environment with development
features, you should be able to compile any of the examples directly
from a terminal just by including C++11 flags in the command for the
compiler:
and tells me to compile using this command: g++ -std=c++0x MY_CODE.cpp -o MY_APP.
Now, what I'm wondering, what is the point of the std=c++0x flag? Is it required, or can I just run g++ MY_CODE.cpp -o MY_APP?
By default, GCC compiles C++-code for gnu++98, which is a fancy way of saying the C++98 standard plus lots of gnu extenstions.
You use -std=??? to say to the compiler what standard it should follow.
Don't omit -pedantic though, or it will squint on standards-conformance.
The options you could choose:
standard with gnu extensions
c++98 gnu++98
c++03 gnu++03
c++11 (c++0x) gnu++11 (gnu++0x)
c++14 (c++1y) gnu++14 (gnu++1y)
Coming up:
c++1z gnu++1z (Planned for release sometime in 2017, might even make it.)
GCC manual: https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/Standards.html#Standards
Also, ask for full warnings, so add -Wall -Wextra.
There are preprocessor-defines for making the library include additional checks:
_GLIBCXX_CONCEPT_CHECKS to add additional compile-time-checks for some templates prerequisites. Beware that those checks don't actually always do what they should, and are thus deprecated.
_GLIBCXX_DEBUG. Enable the libraries debug-mode. This has considerable runtime-overhead.
_GLIBCXX_DEBUG_PEDANTIC Same as above, but checks against the standards requirements instead of only against the implementations.
You want to use the C++11 standard (and you are right to want that), but C++11 made a huge progress w.r.t. its older C++98 standard.
But old versions of GCC (i.e. GCC 4.8 or earlier) where not finalized before the standard itself (so they accepted the -std=c++0x flag). I strongly recommend (if you want C++11) to use the latest version of GCC, that is GCC 4.9. A bug fixing GCC 4.9.2 release appeared at end of october 2014. So use it please, and pass it the std=c++11 flag to tell the compiler you want C++11 conformance.
I actually suggest to pass std=c++11 -Wall -Wextra -g to get C++11, all warnings, and debug info. Once you have debugged your program (with gdb, and you'll better also use a recent version of gdb!) you might ask the compiler to optimize with -O2 (and perhaps -mtune=native if you want to optimize for your own computer)
Source for your reference:
main.cpp
#include <iostream>
using namespace std;
int main()
{
cout << "Test main CPP" << endl;
return 0;
}
build.sh
rm demoASI*
echo "**cleaned !!**"
##### C++ 11 Compliance #####
# type ONE
g++ -o demoASI_1 -std=c++0x main.cpp
echo "**rebuild-main-done (C++ 11 Compilation) !**"
# type TWO
g++ -o demoASI_2 -std=c++11 main.cpp
echo "**rebuild-main-done (C++ 11 Compilation) !**"
##### C++ 11+ Compliance #####
# type THREE
g++ -o demoASI_3 -std=c++1y main.cpp
echo "**rebuild-main-done (C++ 11+ (i.e. 1y, but not C++14) Compilation) !**"
###### C++ 14 Compliance ######
# type FOUR
g++ -o demoASI_4 -std=c++14 main.cpp
if [ $? -eq 0 ]
then
echo "**rebuild-main-done (C++ 14 Compilation) !** :: SUCCESS"
else
echo "**rebuild-main-done (C++ 14 Compilation) !** :: FAILED"
fi
Now, execute the script as;
./build.sh (assuming build.sh has execution permission)
You can first check the version of your g++ compiler, as;
g++ --version
The version of g++, after 4.3, has support for the c++11.
Please see, for c++14 support info in compiler.
I'm trying to change the settings of g++ from the Code::Blocks IDE. I went to the Settings tab, clicked Compiler... and checked various options for the compiler to use, like
Enable all warnings (-Wall)
Have g++ follow the C++11 ISO C++ language standard (-std=c++11)
......
These are just two of many others; when I compile on the command line, here is what comes up:
g++ -o example example.cpp
# warning: initializer lists only available with -std=c++11 ...
Notice how there's no warning either - I have an unused variable in my program. It only works if I give the options manually:
g++ -Wall -std=c++11 -o example example.cpp
Do you think I might have done something wrong when setting up the compiler? Why aren't the options taking affect?
Invoking the compiler from the ide is completely independent from doing it in a command line shell. There's no reason for the setting and usage of one to have any effect on the other.
I'm running Windows 7 with cygwin installed and trying to have a play around with some of the newer C++ features. I'm aware that in order to enable these features I have to pass g++ the -std=c++0x flag, however that gives me the following error:
cc1plus: error: unrecognized command line option "-std=c++0x"
The command line I'm issueing that gives rise to that error is:
g++-3 hello.cpp -std=c++0x -o hello
The reason for the g++-3 is because windows has trouble with the symbolic link. I've used g++ in the cygwin terminal and the result is the same anyway.
Any ideas?
You need to be using a version of GCC which supports C++ 2011 features.
This page has a list of compilers and which features each one supports. If I were you, I'd try to use GCC 4.7 if at all possible.