Can't run to_string() function on Linux - c++

I've got some code that I'm running on Mac OS X that can't be compiled on the Virtual Machine running Linux Mint. This is a simple example. When I run it in Mac, all is fine, but I'm getting issues when I run the same code on Linux, so I'm assuming the library I'm including is not there, but should I be getting an include error then?
Here's the example code that runs on Mac.
#include <iostream>
#include <stdlib.h>
#include <string>
#include <cstdlib>
using namespace std;
int main(){
for (int i = 0; i < 10; i++){
string test = to_string(i);
cout << test << endl;
}
cout << "done" << endl;
return 0;
}
I get no issues here but running on Linux Mint, I get this when I try to compile:
for.cpp: In function 'int main()':
for.cpp:7:28 error: 'to_string' was not declared in this scope
string test = to_string(i);
^
make: *** [for] Error 1
Am I missing something? Any help would be much appreciated!
edit
I realize I forgot to include <string> on here and I fixed it, but what I changed (<string> included) still doesn't compile on Linux. I've used to_string before. I know that much in C++. I also tried adding <cstdlib>. Once again, this DOES compile on Mac and DOES NOT compile on Linux.
Here is my OSX output:
0
1
2
3
4
5
6
7
8
9
done
Here is my output on Linux Mint (Once again, Virtual Box, g++ make):
test.cpp: In function ‘int main()’:
test.cpp:9:28: error: ‘to_string’ was not declared in this scope
string test = to_string(i);
^
make: *** [test] Error 1
You could reproduce the problem yourself if you don't believe me. It's the same code, you can see for yourself if you want.

Compile your for.cpp file like this:
g++ -std=c++11 for.cpp
and run it with:
./a.out
The support for the to_string function in the <string> header was added in the C++11 version of the language, so you need to tell GCC to use that version. You can use the c++0x flag too, for example:
g++ -std=c++0x for.cpp
And you don't have to worry about <cstdlib>, that has nothing to do with it...
to_string() is defined in <string> if you are compiling with C++11 (but is not defined, or unreliably defined as an extension feature, if you are compiling with an earlier version of C++).
Reference: http://en.cppreference.com/w/cpp/string/basic_string/to_string

SOLUTION:
I found a better solution. For some reason, I've read stdlib.h will not work on some linux systems. I used a different function to convert int to string.
on linux:
#include <stdio.h>
and then
for (int i = 0; i < 10; i++){
char buffer[10];
sprintf(buffer,"%d",i);
string stringInt = buffer;
cout << stringInt << endl;
// do whatever you want with the string
}
edit
To the person that down voted my solution to this, here's a post from six years ago basically saying the same thing.

Related

Simple thread example doesn't work in MinGW

#include <iostream>
#include <thread>
using namespace std;
void thread_c() {
for (int i = 0; i < 11; ++i) {
cout << i;
}
}
int main() {
thread t(thread_c);
t.join();
return 0;
}
Such simple example, but it doesn't work on my g++ (MinGW.org GCC-6.3.0-1) 6.3.0, Windows 8.1
Here's the error:
main.cpp: In function 'int main()':
main.cpp:13:5: error: 'thread' was not declared in this scope
thread t(thread_c);
^~~~~~
main.cpp:14:5: error: 't' was not declared in this scope
t.join();
^
*I've been working on a big project, and noticed about some compilation errors. I wrote this code for testing my compiler out
What's wrong with it?
Loking at your code and the compiler results I see the following:
#include <thread> is not including a file that defines thread as your code expects
GCC 6.3.0 is very old (current is 10.2.0), and chances are it was built without POSIX thread support (and probably only support for Windows threads)
I always recommend using MinGW-w64 instead of MinGW as it is more up to date and supports both 32-bit and 64-bit Windows.
When I build your example with the MinGW-w64 from http://winlibs.com/ (which has POSIX thread support) I get no errors and the example works (output is 012345678910).

Trivial Eigen3 Tensor program does not build without -On

I'm trying to build a write of software with the Tensor module provided as unsupported from eigen3. I've written a simple piece of code that will build with a simple application of VectorXd (just printing it to stdout), and will also build with an analogous application of Tensor in place of the VectorXd, but WILL NOT build when I do not throw an optimization flag (-On). Note that my build is from within a conda enviromnent that is using conda-forge compilers, so the g++ in what follows is the g++ obtained from conda forge for ubuntu. It says its name in the error messages following, if that is perceived to be the issue.
I have a feeling this is not about the program I'm trying to write, but just in case I've included an mwe.cpp that seems to produce the error. The code follows:
#include <eigen3/Eigen/Dense>
#include <eigen3/unsupported/Eigen/CXX11/Tensor>
#include <iostream>
using namespace Eigen;
using namespace std;
int main(int argc, char const *argv[])
{
VectorXd v(6);
v << 1, 2, 3, 4, 5, 6;
cout << v.cwiseSqrt() << "\n";
Tensor<double, 1> t(6);
for (auto i=0; i<v.size(); i++){
t(i) = v(i);
}
cout << "\n";
for (auto i=0; i<t.size(); i++){
cout << t(i) << " ";
}
cout << "\n";
return 0;
}
If the above code is compiled without any optimizations, like:
g++ -I ~/miniconda3/envs/myenv/include/ mwe.cpp -o mwe
I get the following compiler error:
/home/myname/miniconda3/envs/myenv/bin/../lib/gcc/x86_64-conda_cos6-linux-gnu/7.3.0/../../../../x86_64-conda_cos6-linux-gnu/bin/ld: /tmp/cc2q8gj4.o: in function `Eigen::internal::(anonymous namespace)::get_random_seed()':
mwe.cpp:(.text+0x15): undefined reference to `clock_gettime'
collect2: error: ld returned 1 exit status
If instead I ask for 'n' optimization level, like the following:
g++ -I ~/miniconda3/envs/loos/include/ -On mwe.cpp -o mwe
The program builds without complaint and I get expected output:
$ ./mwe
1
1.41421
1.73205
2
2.23607
2.44949
1 2 3 4 5 6
I have no clue why this little program, or the real program I'm trying to write, would be trying to get a random seed for anything. Any advice would be appreciated. The reason why I would like to build without optimization is so that debugging is easier. I actually thought all this was being caused by debug flags, but I realized that my build tool's debug setting didn't ask for optimization and narrowed that down to the apparent cause. If I throw -g -O1 I do not see the error.
Obviously, if one were to comment out all the code that has to do with the Tensor module, that is everthing in main above 'return' and below the cwiseSqrt() line, and also the include statement, the code builds and produces expected output.
Technically, this is a linker error (g++ calls the compiler as well as the linker, depending on the command line arguments). And you get linker-errors if an externally defined function is called from somewhere, even if the code is never reached.
When compiling with optimizations enabled, g++ will optimize away uncalled functions (outside the global namespace), thus you get no linker errors. You may want to try -Og instead of -O1 for better debugging experience.
The following code should produce similar behavior:
int foo(); // externally defined
namespace { // anonymous namespace
// defined inside this module, but never called
int bar() {
return foo();
}
}
int main() {
// if you un-comment this line, the
// optimized version will fail as well:
// ::bar();
}
According to man clock_gettime you need to link with -lrt if your glibc version is older than 2.17 -- maybe that is the case for your setup:
g++ -I ~/miniconda3/envs/myenv/include/ mwe.cpp -o mwe -lrt

eclipse CDT issue on Mac OSX

On one of my Mac box, for simple Hello Word C++ program, there are such compile error, other Macs I am working on are ok. Using even the same version of Eclipse CDT 64-bit Mars.
Posted error and Hello Word program, does anyone have any hints? Thanks.
//============================================================================
// Name : Test1.cpp
// Author :
// Version :
// Copyright : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================
#include <iostream>
using namespace std;
int main() {
cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!
return 0;
}
Attach error from g++ of command line,
g++ Test1.cpp
Test1.cpp:9:20: error: iostream: No such file or directory
Test1.cpp: In function ‘int main()’:
Test1.cpp:13: error: ‘cout’ was not declared in this scope
Test1.cpp:13: error: ‘endl’ was not declared in this scope
In summary, if whether you're developing in C, C++ or Objective C on the Mac, you probably just want to use XCode.
Not sure what Eclipse was doing, but (see link in comments) earlier versions of Eclipse might work where later ones will not.

Getting compiler to work in Notepad++

I'm having some trouble using Notepad++ to compile code. I've installed notepad++ (and NppExec), downloaded MinGW from this source (http://nuwen.net/mingw.html) and installed it to "C:\MinGW\".
Then I tried to set notepad++ to use g++ to compile c++. Per advice, I entered the following into NppExec's console:
NPP_SAVE
CD $(CURRENT_DIRECTORY)
C:\MinGW\bin\g++.exe -g "$(FILE_NAME)"
Saved it as C++ Compiler, and added it to the "Macros" section of the toolbar.
Then I tried to run a simple test program:
#include <iostream>
int main()
{
cout << "Hello, world!";
}
After that a couple of weird errors popped up. First it wanted me to save to System32 by default, which I don't remember it doing before (it won't let me, forcing me to save in Documents).
I let it save to documents, than tried to run it with the compiler. It gives me this error, which I don't recognize at all:
NPP_EXEC: "C++ Compiler"
NPP_SAVE: C:\Users\Bova\Documents\Test.cpp
CD: C:\Users\Bova\Documents
Current directory: C:\Users\Bova\Documents
C:\MinGW\bin\g++.exe -g "Test.cpp"
Process started >>>
Test.cpp: In function 'int main()':
Test.cpp:5:5: error: 'cout' was not declared in this scope
cout << "Hello, world!";
^
Test.cpp:5:5: note: suggested alternative:
In file included from Test.cpp:1:0:
c:\mingw\include\c++\4.8.2\iostream:61:18: note: 'std::cout'
extern ostream cout; /// Linked to standard output
^
<<< Process finished. (Exit code 1)
Please help.
There is nothing wrong with your compiler. You are not using the correct namespace to use cout
#include <iostream>
int main()
{
std::cout << "Hello, world!";
}
Or
#include <iostream>
using namespace std;
int main()
{
cout << "Hello, world!";
}

Why are std::stoi and std::array not compiling with g++ c++11?

I've been learning C++ and using the Terminal for the last couple of months. My code was compiling and running fine using g++ and C++11, but in the last couple of days it started giving errors and I have had problems compiling since. The only programs I can compile and run depend on older C++ standards.
The errors I first got related to #include < array > in the header file. Not sure why this happened, but I got around it by using boost/array instead. Another error I can't solve is with std::stoi. Both array and stoi should be in the C++11 standard library. I made the following simple code to demonstrate what's going on:
//
// stoi_test.cpp
//
// Created by ecg
//
#include <iostream>
#include <string> // stoi should be in here
int main() {
std::string test = "12345";
int myint = std::stoi(test); // using stoi, specifying in standard library
std::cout << myint << '\n'; // printing the integer
return(0);
}
Try to compile using ecg$ g++ -o stoi_trial stoi_trial.cpp -std=c++11
array.cpp:13:22: error: no member named 'stoi' in namespace 'std'; did you mean
'atoi'?
int myint = std::stoi(test);
~~~~~^~~~
atoi
/usr/include/stdlib.h:149:6: note: 'atoi' declared here
int atoi(const char *);
^
array.cpp:13:27: error: no viable conversion from 'std::string' (aka
'basic_string') to 'const char *'
int myint = std::stoi(test);
^~~~
/usr/include/stdlib.h:149:23: note: passing argument to parameter here
int atoi(const char *);
^
2 errors generated.
I also get these errors at compilation when using gcc or clang++ and with -std=gnu++11 (I guess they all depend on the same file structure). I also get the same error whether I specify std:: in the code, or if I specify using namespace std;
I worry that these issues arose because of the September Command Line Tools update via Xcode or because I installed boost and this somehow messed up my C++11 libraries. Hopefully there is a simple solution.
My system:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-> dir=/usr/include/c++/4.2.1
Apple LLVM version 5.0 (clang-500.2.76) (based on LLVM 3.3svn)
Target: x86_64-apple-darwin12.5.0
Thread model: posix
Thanks for any insight you can offer.
clang has a weird stdlib, you need to add the following flag when you compile
-stdlib=libc++
your snippet works on my mac with
g++ -std=gnu++11 -stdlib=libc++ test.cpp -o test
This answer describes the problem