初始化具有动态长度的向量

Question

Can you please tell me how to change the size of the buf vector into a dynamic length?

long five = 555;
char buf[256];
snprintf(buf, sizeof(buf), "%d", five); 

THX!

How to change my code with std::vector<std::string>buf; in order to work correctly?
I have error:

vector is not a member of std;
buf was not declared in this scope and error: expected primary-expression before ">" token

Answer 1

In C++, you can't. You will have to allocate it dynamically somehow, or better still use a dynamic data structure like a std::vector.

Answer 2

Try:

#include <vector>
#include <string>

long five = 555;

// using vector
std::vector<char> buf1(256);
snprintf(&buf1[0], buf1.size(), "%d", five);

// Or using string 
std::string       buf2(256);
snprintf(&buf2[0], buf2.size(), "%d", five);

Though rather than using snprintf() I would look up how to use stringstream.

Answer 3

if you're really opposed to using the vector class, you could implement the dynamic memory yourself. Create a function for adding to the array when theres not enough memory to store the new values. It would malloc new memory, copy the contents over, append new values, delete the old memory, then return a pointer to the new array. They amount new memory that you would use would depend on your application.(ie. just enough memory to store new values to conserve memory, or a lot more(eg double) than the old size so you wouldn't have to call this function as often.

Answer 4

You probably want to make a vector of characters, not a vector of strings.

The second error I suspect is a missing space character before the variable name.