I'm trying to compile and strip a very simple programm in C++ with the g++ compiler (4.6.0 on Mac OSX). But while compiling i get an warning.
source code:
#include </usr/local/Cellar/gcc/4.6.0/gcc/include/c++/4.6.0/iostream>
int main(){
std::cout << ("Hello World\n") ;
}
Terminal code:
g++ hello.cc -Wall -std=c++0x -s
/* or an alternative: */
g++ hello.cc -Wall -std=c++0x -o test -Wl,-s
Compiler warning:
ld: warning: option -s is obsolete and being ignored
Somebody any idea's about this weird warning?
Edit:
The weird thing is the size does decrease when using the -s flag, the decreases from 9,216 bytes to 9,008.
However when i use the following the size decreases to 8,896 bytes.
cp hello hello_stripped
strip hello_stripped
The error message is from ld, not from gcc or g++. (The gcc and g++ commands are a drivers that invokes the compiler, the linker, and other tools.)
gcc passes the -s option to the linker, as documented in the gcc 4.6.1 manual; apparently the MacOS port of gcc still does that.
The GNU linker (GNU ld) still accepts the -s option with its usual meaning. But the MacOS linker (also called ld) ignores it, as documented in the MacOS ld manual:
-s Completely strip the output, including removing the symbol table.
This file format variant is no longer supported. This option is
obsolete.
And the MacOS gcc manual, unlike GNU's gcc manual, doesn't mention "-s".
Apparently the -s flag is obsolete. You can use the strip program instead though.
Related
warning: unknown pragma ignored [-Wunknown-pragmas]
#pragma GCC optimize("O3")
I want to enable GCC optimization flags, but they are ignored when i'm compiling code, although they are present in documentation. Why does this happen?
The problem was that g++ is a clang alias in MacOS by default
So i did this
cd /usr/local/bin
ln -s g++-11 g++
this fixes the problem and g++ command will run actual gcc compuler instead of clang
Consider the following code lying in main.cpp:
#include <iostream>
int main() {
std::cout << "Hello World!\n";
}
Compilation with g++ main.cpp -o -main fails:
/usr/bin/ld: unrecognised emulation mode: ain
Supported emulations: elf_x86_64 elf32_x86_64 elf_i386 elf_iamcu elf_l1om elf_k1om i386pep i386pe
collect2: error: ld returned 1 exit status
I'm on a 64-bit Ubuntu 20.04.3 LTS running in WSL2. GCC's version is
g++ (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
How do I make this Hello World compile?
You've accidentally typed a dash before specifying your output file: it should be -o main, not -o -main, so the full command line is g++ main.cpp -o main
GCC has a -m key which allows specifying target machine architecture. For some reason, even when -main immediately follows -o, GCC still checks that the architecture (ain in case of -main) exists.
For example, if I compile with g++ main.cpp -o -melf_x86_64, I get an executable named -melf_x86_64 (to remove it, use rm ./-melf_x86_64 instead of rm -melf_x86_64). However, if I try g++ main.cpp -o -mi386, I get some compilation errors because I don't have 32-bit C++ standard library installed.
Looks like a bug to me: it simultaneously changes target architecture AND changes output file name. I've just opened GCC issue and LLVM issue (clang is affected as well).
UPD: actually looks like a bug in LD.
I'm trying to configure eclipise kepler to use c++ 11.
I appended -std=c++11 to:
Properties > c/c++ build > settings > GCC c++ complier > Miscellaneous>other flags
But when I compile the project it says:
compilation terminated. /bin/sh: 1: -std=c++11: not found
I'm using gcc on ubuntu,
any ideas?
Flags (or compiler options) are nothing but ordinary command line arguments passed to the compiler executable.
Assuming you are invoking g++ from the command line (terminal):
$ g++ -Wall -g -std=c++11 your_file.cpp -o your_program
or
$ g++ -Wall -g -std=c++0x your_file.cpp -o your_program
if the above doesn't work.
So in your case if -std=c++11 does not work, try -std=c++0x
Another source for this error could be an old compiler version.
Type gcc --version into the terminal and check the version. Here is a quick overview which version is capable of c++11:
C++11 Support in GCC
GCC 4.8.1 was the first feature-complete implementation of the 2011
C++ standard, previously known as C++0x.
This mode can be selected with the -std=c++11 command-line flag, or
-std=gnu++11 to enable GNU extensions as well.
Link: https://gcc.gnu.org/projects/cxx-status.html
I'm taking part in a programming contest and the requirement is that code will be compiled using following command:
g++ -std=c++11 -O2 -o a.out orienteering.cpp
How do I check if my code works for this command? (I use DevC++ for coding and it has automatic compilation).
Also compiler should be GCC 4.8.2 or later. What does this mean? Is my older GCC version (4.7.2) not suitable?
You check your code by placing it in a file named orienteering.cpp, and running this command in the same directory:
g++ -std=c++11 -O2 -o a.out orienteering.cpp
If the compiler spits out any messages at all then you have a problem. If the compiler is silent and creates a file named a.out, then all is well.
GCC 4.7.2 does not meet the criteria "GCC 4.8.2 or later".
I have installed Clang by using apt-get in Ubuntu, and I can successfully compile C files using it. However, I have no idea how to compile C++ through it. What do I need to do to compile C++?
The command clang is for C, and the command clang++ is for C++.
I do not know why there is no answer directly addressing the problem. When you want to compile C++ program, it is best to use clang++, instead of using clang. For example, the following works for me:
clang++ -Wall -std=c++11 test.cc -o test
If compiled correctly, it will produce the executable file test, and you can run the file by using ./test.
Or you can just use clang++ test.cc to compile the program. It will produce a default executable file named a.out. Use ./a.out to run the file.
The whole process is a lot like g++ if you are familiar with g++. See this
post to check which warnings are included with -Wall option. This
page shows a list of diagnostic flags supported by Clang.
A note on using clang -x c++: Kim Gräsman says that you can also use
clang -x c++ to compile CPP programs, but that may not be always viable. For example, I am having a simple program below:
#include <iostream>
#include <vector>
int main() {
/* std::vector<int> v = {1, 2, 3, 4, 5}; */
std::vector<int> v(10, 5);
int sum = 0;
for (int i = 0; i < v.size(); i++){
sum += v[i]*2;
}
std::cout << "sum is " << sum << std::endl;
return 0;
}
clang++ test.cc -o test will compile successfully, but clang -x c++ will
not, showing a lot of undefined reference errors. So I guess they are not exactly equivalent. It is best to use clang++ instead of clang -x c++ when compiling c++ programs to avoid extra troubles.
clang version: 11.0.0
Platform: Ubuntu 16.04
Also, for posterity -- Clang (like GCC) accepts the -x switch to set the language of the input files, for example,
$ clang -x c++ some_random_file.txt
This mailing list thread explains the difference between clang and clang++ well: Difference between clang and clang++
Solution 1:
clang++ your.cpp
Solution 2:
clang your.cpp -lstdc++
Solution 3:
clang -x c++ your.cpp
I've had a similar problem when building Clang from source (but not with sudo apt-get install. This might depend on the version of Ubuntu which you're running).
It might be worth checking if clang++ can find the correct locations of your C++ libraries:
Compare the results of g++ -v <filename.cpp> and clang++ -v <filename.cpp>, under "#include < ... > search starts here:".
Open a Terminal window and navigate to your project directory. Run these sets of commands, depending on which compiler you have installed:
To compile multiple C++ files using clang++:
$ clang++ *.cpp
$ ./a.out
To compile multiple C++ files using g++:
$ g++ -c *.cpp
$ g++ -o temp.exe *.o
$ ./temp.exe