to_string is in std::

src/ansi-c/ansi_c_entry_point.cpp

@@ -51,7 +51,7 @@ exprt::operandst build_function_environment(
   for(const auto & p : parameters)
   {
     irep_idt base_name=p.get_base_name().empty()?
-      ("argument#"+to_string(i)):p.get_base_name();
+      ("argument#"+std::to_string(i)):p.get_base_name();
     irep_idt identifier=id2string(goto_functionst::entry_point())+
       "::"+id2string(base_name);
 

src/goto-programs/graphml_witness.cpp

@@ -415,7 +415,7 @@ void graphml_witnesst::operator()(const symex_target_equationt &equation)
 
     const graphmlt::node_indext node=graphml.add_node();
     graphml[node].node_name=
-      i2string(it->source.pc->location_number)+"."+i2string(step_nr);
+      std::to_string(it->source.pc->location_number)+"."+std::to_string(step_nr);
     graphml[node].file=source_location.get_file();
     graphml[node].line=source_location.get_line();
     graphml[node].thread_nr=it->source.thread_nr;

src/path-symex/path_symex.cpp

@@ -8,6 +8,7 @@ Author: Daniel Kroening, kroening@kroening.com
 
 #include <util/arith_tools.h>
 #include <util/simplify_expr.h>
+#include <util/string2int.h>
 #include <util/byte_operators.h>
 #include <util/pointer_offset_size.h>
 #include <util/expr_util.h>
@@ -368,7 +369,7 @@ void path_symext::symex_va_arg_next(
        */
       if(has_prefix(id2string(id), base))
         id=base
-            +i2string(
+            +std::to_string(
                 safe_string2unsigned(
                     std::string(id2string(id), base.size(), std::string::npos))
                     +1);
@@ -787,7 +788,7 @@ void path_symext::function_call_rec(
         exprt rhs=*call_arguments_it;
 
         irep_idt id=id2string(function_identifier)+"::va_arg"
-            +i2string(va_count);
+            +std::to_string(va_count);
 
         symbolt symbol;
         symbol.name=id;