Working with TString

ROOT
1

Hi,
as in the listing, the string cant be printed normally whenever I passed a string through argv[] to label1 or label2.
but the case3 succeed. How to pass stored string or TString into Form() ?

int main( int argc, char* argv[] ){
	TString label1 = Form("_%s",argv[1]); // this failed

	std::string label2 = argv[1]; // this failed

	TString ResultsName("");
	ResultsName.Form("results/TrainingResult%s.root",label1);
	std::cout << ResultsName << std::endl;
	
	// case 3: worked
	TString s("a=");
	s.Form("This is %s string w/ a %d and a %f", "a", 5, 3.14);
	std::cout << s << std::endl;

Please read tips for efficient and successful posting and posting code

_ROOT Version: 6.24 (PyROOT via conda)
_Platform:Centos7
_Compiler: gcc9

2

Are you trying to use it as a ROOT macro?
Well, “int main( int argc, char* argv[])” suggests that you are building a compiled executable.

3

exactly. and i have included the (sorry for skipping that part)

4

What “exactly”?

5

i am building an executable program using the code

6

Can you post a complete “minimal reproducer” (so that we can try it).

7 
#include <iostream>

#include "TChain.h"
#include "TFile.h"
#include "TTree.h"
#include "TString.h"
#include "TObjString.h"
#include "TSystem.h"
#include "TROOT.h"

#include "TMVA/Factory.h"
#include "TMVA/DataLoader.h"
#include "TMVA/Tools.h"
#include "TMVA/TMVAGui.h"


int main( int argc, char* argv[] ){
	TString label1 = Form("_%s",argv[1]); // this failed

	std::string label2 = argv[1]; // this failed

	TString ResultsName("");
	ResultsName.Form("results/TrainingResult%s.root",label1);
	std::cout << ResultsName << std::endl;
	
	// case 3: worked
	TString s("a=");
	s.Form("This is %s string w/ a %d and a %f", "a", 5, 3.14);
	std::cout << s << std::endl;    
}

FYI, i am currently working on codes involving string and TSTrings. i removed the part from TMVA training (which I adapted from the example Classification.C), now i am working to take external args into parameters that go into the TMVA training

8

So you can either use

   TString label1 = Form("_%s",argv[1]);
[...]
   ResultsName.Form("results/TrainingResult%s.root",label1.Data());

or

   std::string label2 = argv[1];
[...]
   ResultsName.Form("results/TrainingResult%s.root",label2.c_str());
9

thanks. Both worked.
Could you simply explain what’s going on my code and the solution if possible ?

10

You should have got an explicit note (from the compiler) in the form:
main.cxx:23:50: warning: format ‘%s’ expects argument of type ‘char*’, but argument 3 has type ‘TString’ [-Wformat=]
So, it’s clear you need “label1.Data()” there.

11

actually my code compiled successfully. here is the make command:

g++ training.cpp -Wl,--no-as-needed -pthread -std=c++17 -m64 -I/home/user/.conda/envs/testroot/include -ggdb -L/home/user/.conda/envs/testroot/lib -lCore -lImt -lRIO -lNet -lHist -lGraf -lGraf3d -lGpad -lROOTVecOps -lTree -lTreePlayer -lRint -lPostscript -lMatrix -lPhysics -lMathCore -lThread -lMultiProc -lROOTDataFrame -Wl,-rpath,/home/user/.conda/envs/testroot/lib -pthread -lm -ldl -rdynamic -lMLP -lMinuit -lTreePlayer -lTMVA -lTMVAGui -lXMLIO  -lMLP -lm -o training.out

the problem arises when i run the training.out

12

Form("%s") requires a const char * argument, not a TString, nor a std::string. TString::Data() and std::string::c_str() return both a const char *