Fix string indexing #273

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1. namannimmo10 commented on Mar 23, 2022

   

   namannimmo10

   on Mar 23, 2022

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   C++ code for reference:

   #include <iostream>
   #include <string>
   #include <vector>
   #include <cassert>
   #include <cmath>
   #include <Kokkos_Core.hpp>
   #include <lfortran_intrinsics.h>
   
   template <typename T>
   Kokkos::View<T*> from_std_vector(const std::vector<T> &v)
   {
       Kokkos::View<T*> r("r", v.size());
       for (size_t i=0; i < v.size(); i++) {
           r(i) = v[i];
       }
       return r;
   }
   
   void _lpython_main_program()
   {
       f();
   }
   
   void f()
   {
       std::string s;
       s = "abcdefg";
       std::cout << s[1 + 1-1] << std::endl;
       std::cout << s[2 + 1-1] << std::endl;
       std::cout << s[3 + 1-1] << std::endl;
   }
   
   namespace {
   
   void main2() {
           _lpython_main_program();
   }
   
   }
   int main(int argc, char* argv[])
   {
       Kokkos::initialize(argc, argv);
       main2();
       Kokkos::finalize();
       return 0;
   }
2. namannimmo10 commented on Mar 23, 2022

   

   namannimmo10

   on Mar 23, 2022

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   We should improve it as well.
3. namannimmo10 commented on Mar 26, 2022

   

   namannimmo10

   on Mar 26, 2022

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   I guess the problem is here:

   lpython/src/libasr/codegen/asr_to_llvm.cpp

   Lines 1029 to 1043 in 3104565

   	if (l == r) {
   	this->visit_expr_wrapper(x.m_args[0].m_left, true);
   	llvm::Value *idx = tmp;
   	idx = builder->CreateSub(idx, llvm::ConstantInt::get(context, llvm::APInt(32, 1)));
   	//std::vector<llvm::Value*> idx_vec = {llvm::ConstantInt::get(context, llvm::APInt(32, 0)), idx};
   	std::vector<llvm::Value*> idx_vec = {idx};
   	llvm::Value *str = builder->CreateLoad(array);
   	llvm::Value *p = builder->CreateGEP(str, idx_vec);
   	// TODO: Currently the string starts at the right location, but goes to the end of the original string.
   	// We have to allocate a new string, copy it and add null termination.
   	tmp = builder->CreateAlloca(character_type, nullptr);
   	builder->CreateStore(p, tmp);
   	//tmp = p;
4. Smit-create commented on Apr 14, 2022

   

   Smit-create

   on Apr 14, 2022

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   This issue might be easier to handle once we move forward with: https://gitlab.com/lfortran/lfortran/-/merge_requests/1700

   👍React with 👍1Reacted by Naman Gera
5. certik

   closed this as completedin #423on May 1, 2022