dynamic memory allocation of strings in cpp

Question

so here's the thing I've been working on a code for 5 hours now and logic looks good the program seems to do it's job, the only thing that keeps bugging me is dynamic memory allocation of strings. The question does not specify the initial number of strings user has to enter. Here's what I've been trying to do to dynamically take the strings :

      int t;
      cin>>t  //number of strings user wishes enter 
      char *s1[1000009];  //1000009 is the maximum number of digits each string can have
      for(i=0;i<t;i++)
      {
                s1[i]=(char *)malloc(1000009) 
                cin>>s1[i];
      }

not sure if it is the right way or not. A way through which i could store a 2D character array would also do if not dynamic strings.

Thanking you, gaurav

Don't use malloc for manual dynamic allocation. Use new instead. Don't use manual dynamic allocation at all. Use std::string instead. — eerorika
– eerorika, Commented Nov 5, 2015 at 15:59

Kevin · Accepted Answer · 2015-11-05 16:07:52Z

5

Use a vector of strings instead of using malloc/new.

int t;
std::cin >> t;
std::vector<std::string> strings(t); //Create t strings
for(int i = 0; i < t; i++)
    std::cin >> strings[i]; //Read into each string

answered Nov 5, 2015 at 16:07

Kevin

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4 Comments

gaurav21 Over a year ago

sir that works like a charm thank you, clearly I've got a lot to learn on vectors !

gaurav21 Over a year ago

well apparently it did work for the first time now it's just depicting runtime error which says : terminate called after throwing an instance of 'std::bad_alloc' what(): std::bad_alloc

Kevin Over a year ago

Make sure that t is valid. std::vector takes an unsigned value for the size so if t is negative the unsigned value will be very large.

gaurav21 Over a year ago

pretty sure t is never negative :3

Thomas Sparber · Accepted Answer · 2015-11-05 16:07:27Z

1

Since you tagged this question as C++ I would do it like this:

std::vector<std::string> s1(1000009);

That's all - no need to use malloc, no need to take care about destruction. If you are using C++ use the Tools you have available.

answered Nov 5, 2015 at 16:07

Thomas Sparber

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Comments

Thomas Grockowiak · Accepted Answer · 2015-11-05 16:05:59Z

0

i would do it like this :

int i = 0;
char **s1;
s1 = (char **)malloc(t * sizeof(char *));
while (i < t)
{
 s1[i] = (char *)malloc(1000009 * sizeof(char));
 i++;
}

the first malloc create you t line. The second one fill alloc 100000009charactere for each lines

edited Nov 5, 2015 at 16:05

answered Nov 5, 2015 at 16:00

Thomas Grockowiak

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5 Comments

Thomas Grockowiak Over a year ago

but as said above, a vector of std::string would be more efficiency.

gaurav21 Over a year ago

as he said doesn't compile, and I've still got no clue how vectors work any way using malloc or new would be great

Thomas Grockowiak Over a year ago

std::string test; std::vector<std::string> vec; int t; int i = 0; std::cin >> t; while(i < t) { std::cin>> test; i++; vec.push_back(test); test.clear(); }</code>

gaurav21 Over a year ago

@ThomasGrockowiak yes works fine using vectors Thank You !

gaurav21 Over a year ago

sorry to bother you again, the code seems to work fine but it takes a lot of time here take a look, link

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