CODEWITHSUNDEEP
c++
dvrer
dvrer

Reputation: 629

Add char to a String and delete the char array

Is adding a char from a char* to a std::string and then delete[] the char array can cause UB?

or is it safe to process the string after the delete[] ?

int buffer_size = 4096;
char* buffer = new char[buffer_size];

//here there was removed code that assign values to the buffer[i]    

std::string data;

for (int i = 0; i < buffer_size ; i++)
{
    data.push_back(buffer[i]);
}

delete[] buffer;

//is the data string content secured at this point?

Upvotes: 4

Views: 378

Answers (5)

taskinoor
taskinoor

Reputation: 46027

Deleting after creating the string is fine as push_back copies the data. However, a better method is to use simply:

std::string data(buffer, buffer_size);

Calling push_back in a loop may trigger memory allocation multiple times. But with the constructor whole buffer_size memory is allocated at once.

Upvotes: 5

Lukas Schulte
Lukas Schulte

Reputation: 161

The definition of the push_back function is 

void push_back( CharT ch );

As the parameter ch is passed by value and not by reference, it is copied into the string, therefore deleting the source of the char you appended to the string does not cause any issues.

Upvotes: 5

Alex
Alex

Reputation: 1021

yes, its fine, cause you copy chars from buffer to data, so there is no link between two variables after copy is completed. Also you should consider more effective option to copy char* to string, for example this one http://www.cplusplus.com/reference/string/string/operator+=/

Upvotes: 3

lubgr
lubgr

Reputation: 38267

You can see from the signature of std::string::push_back

 void push_back( CharT ch );

that the function argument is copied. Hence, deleting any resource that owned the char after it has been copied into some string is fine.

Note that you can also avoid the manual looping by

data.insert(data.end(), buffer, buffer + buffer_size);

Upvotes: 3

Gojita
Gojita

Reputation: 500

It's safe. But you may also use std::string::append(const char*s , size_t n);

Upvotes: 3

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