Array and Vector difference to use in programming

Question

I have one problem to use std::vector instead of std::array. Most people says they serve for same purpose except their way of memory allocation (array allocates memory statically for its elements and vector allocates memory dynamically ). To clear my understanding I tried something but failed.

I had my running code using array was working fine.

char userInput[MAX_DATA] = { '\0' }; 
std::cout<<"\enter some char: ";
std::cin.getline(userInput, MAX_DATA);
int bytes_sent = send(socketFD, userInput, strlen(userInput), 0);
//send function definition send(__in SOCKET s, __in_bcount(len) const char FAR * buf, __in int len, __in int flags);

By using vector I have changed my code lines by instead of above defined code:

std::vector<char> userbuffer;
std::cout<<"\enter some char: ";
cin>>input;// i only want to send only the data i entered here in run time.
int bytes_sent = send(socketFD, userbuffer, userbuffer.size(), 0);
//error C2664: 'send' : cannot convert parameter 2 from 'std::vector<_Ty>' to 'const char* '

I am really new to c++ STL concepts. Can someone please help me find out what I am doing wrong? My intention to do this is to see dynamic memory allocation.

jrok · Accepted Answer · 2014-01-28 17:32:42Z

4

(I assume send_to takes a char* for 2nd parameter)

std::vector encapsulates a dynamically resizable array. You can get a pointer to the element type taking address of the first element:

&userbuffer[0]

or, since C++11, by calling member function data:

userbuffer.data()

This is guaranteed to work because the internal array is stored contiguously.

answered Jan 28, 2014 at 17:32

jrok

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Comments

James Kanze · Accepted Answer · 2014-01-28 17:48:39Z

2

In addition to what jrok said: there is no operator>> to input into an std::vector<char>. To come closest to what you originally wrote:

std::string userInput;
std::cout << "enter some char: ";
if ( !std::getline( std::cin, userInput ) ) {
    //  Error...
}
int bytesSent = send( socketFG, userInput.data(), userInput.size(), 0 );

(You forgot to check for an error in your initial version as well.)

answered Jan 28, 2014 at 17:48

James Kanze

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2 Comments

User Over a year ago

Thank you ! I faced a run time error because of that but have fixed that:)

User Over a year ago

And in first version i am using if(std::cin.fail()), so that worked fine, i just had problem in second version.

Vlad from Moscow · Accepted Answer · 2014-01-28 17:37:28Z

0

It is better to use class std::string instead of std::vector in this case. You can pass an object of type std::string to the function calling member function c_str()

answered Jan 28, 2014 at 17:37

Vlad from Moscow

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