c_str adds rubbish in the end of char*

Question

I'm building a ftp server and this is a message sent from the client to the server to check whether the file size is approved by the server. I need to use char* in function write so I want to convert string to char*. The string structure is fileName#fileSize(test.txt#37). I tried c_str but got rubbish in the end.

Let have a look at the following code:

string str(filenameDes);
str += HASHTAG;
str += to_string(fileSize);
cout << "str: " << str << endl;
char * pchar = str.c_str();
// sending file size to server
int retVal = write(socket, pchar, strlen(pchar));

Although when i want to print the message in the server using cout i get this output: test2#37�� or something close to it, meaning i get rubbish in the end.

How do i clean the rubbish? or any other command to convert to char* ?

If `str` is a local variable (or otherwise defined in a nested scope) it can go out of scope and the pointer `pchar` becomes invalid. — Some programmer dude, Jun 06 '15 at 11:13
Do you get the "rubbish" in the server, or on the client side? And why not simply do e.g. `write(socket, str.c_str(), str.length())`? — Some programmer dude, Jun 06 '15 at 11:19
And can you please try to create a [Minimal, Complete, and Verifiable Example](http://stackoverflow.com/help/mcve) and show us? — Some programmer dude, Jun 06 '15 at 11:21
i get the rubbish in the server : Message received: test2#378�ѕ� — itzikos, Jun 06 '15 at 11:23
I don't think it is fault of the c_str nor the string class itself... have you debugged it at the client side? — W.F., Jun 06 '15 at 11:32
yes the in the client side the string is fine and also the str.c_str() but when i received it in the server because i don't know the size of the incoming string i have char array of 256 that hold it. I think that the garbage is appearing since there is nothing in the chars in the end of the char array but i dont know how to handle it. — itzikos, Jun 06 '15 at 11:36

score 0 · Answer 1 · answered Jun 06 '15 at 11:45

0

The problem was that when i received the message with array of char i didn't initailize it with \0 in all of the cells. This solves the case when you dont know which length of message you're gonna get. Thanks a lot to PaulMcKenzie.

answered Jun 06 '15 at 11:45

itzikos

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You don't have to initialize *all* data to zero, just terminate the buffer correctly. The `recv` (or `read`) call do return the length of the data received, just do e.g. `buffer[returnOfRecv] = '\0'`. – Some programmer dude Jun 06 '15 at 12:03
Warning to future: This works for an ftp server because the protocol stops and waits for a response. It will not work if multiple messages can be sent without waiting because multiple messages may wind up in the same call to `recv`. There is no way to tell them apart without extra information. – user4581301 Jun 06 '15 at 15:01

c_str adds rubbish in the end of char*

1 Answers1