c++ - What is the right way to handle char* strings? -

i have third party library using char* (non-const) placeholder string values. right , safe way assign values datatypes? have following test benchmark uses own timer class measure execution times:

#include "string.h" #include <iostream> #include <sj/timer_chrono.hpp>  using namespace std;  int main() {     sj::timer_chrono sw;      int iterations = 1e7;      // first method gives compiler warning:     // conversion string literal 'char *' deprecated [-wdeprecated-writable-strings]     cout << "creating c-strings unsafe(?) way..." << endl;     sw.start();     (int = 0; < iterations; ++i)     {         char* str = "teststring";     }        sw.stop();     cout << sw.elapsed_ns() / (double)iterations << " ns" << endl;      cout << "creating c-strings safe(?) way..." << endl;     sw.start();     (int = 0; < iterations; ++i)     {         char* str = new char[strlen("teststr")];         strcpy(str, "teststring");     }        sw.stop();     cout << sw.elapsed_ns() / (double)iterations << " ns" << endl;       return 0;  } 

output:

creating c-strings unsafe(?) way... 1.9164 ns creating c-strings safe(?) way... 31.7406 ns 

while "safe" way get's rid of compiler warning makes code 15-20 times slower according benchmark (1.9 nanoseconds per iteration vs 31.7 nanoseconds per iteration). correct way , dangerous "deprecated" way?

the c++ standard clear:

an ordinary string literal has type “array of n const char” (section 2.14.5.8 in c++11).

and

the effect of attempting modify string literal undefined (section 2.14.5.12 in c++11).

for string known @ compile time, safe way of obtaining non-const char* this

char literal[] = "teststring"; 

you can safely

char* ptr = literal; 

if @ compile time don't know string know length can use array:

char str[str_length + 1]; 

if don't know length need use dynamic allocation. make sure deallocate memory when strings no longer needed.

this work if api doesn't take ownership of char* pass.

if tries deallocate strings internally should in documentation , inform on proper way allocate strings. need match allocation method 1 used internally api.

the

char literal[] = "test"; 

will create local, 5 character array automatinc storage (meaning variable destroyed when execution leaves scope in variable declared) , initialize each character in array characters 't', 'e', 's', 't' , '\0'.

you can later edit these characters: literal[2] = 'x';

if write this:

char* str1 = "test"; char* str2 = "test"; 

then, depending on compiler, str1 , str2 may same value (i.e., point same string).

("whether string literals distinct (that is, stored in nonoverlapping objects) implementation- defined." in section 2.14.5.12 of c++ standard)

it may true stored in read-only section of memory , therefore attempt modify string result in exception/crash.

they also, in reality of type const char* line:

char* str = "test";

actually casts away const-ness on string, why compiler issue warning.