Qt - C++ string concatenation segmentation fault

Question

I'm new to c++, so I guess I fell into a newbyes C++ pitfall.

I tried to do the following:

QString  sdkInstallationDirectory=getenv("somEnv");

QString someSourceDir=sdkInstallationDirectory+"\\Data\\"+someReference+ "\\src";

and I get a segmentation fault.

I guess this is because of the concatenation of the const chars and insufficient memory allocated to the someSourceDir QString.

What exactly is my mistake? How can I do this concatenation?

ForEveR · Accepted Answer · 2012-07-23 14:47:44Z

3

char * getenv ( const char * name );

A null-terminated string with the value of the requested environment variable, or NULL if that environment variable does not exist.

Why you not check result?

EDIT.

So, check pointer is not necessary.

For historical reasons, QString distinguishes between a null string and an empty string. A null string is a string that is initialized using QString's default constructor or by passing (const char *)0 to the constructor.

edited Jul 23, 2012 at 14:47

answered Jul 23, 2012 at 11:19

ForEveR

56.1k2 gold badges127 silver badges139 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

sara Over a year ago

Well, the tool is installed by installer that creates the environment variable. No variable=no tool, I will check it as precaution of course, but it is not the cause. Anyway - great answer, and +1. I found the problem, and it was not related for the question, sorry.

Jens Over a year ago

QString can handle a Null-Pointer construction, the constructor QString(const char*) will create an empty QString with Unicode coding. The code provided by sara is perfectly fine and clear.

Community · Accepted Answer · 2017-05-23 12:03:56Z

-1

You can't add strings together with a +. Try using a stringstream.

Something like:

stringstream ss; ss << sdkInstallationDirectory << "\Data\" + someReference << "\src"; string str = ss.str();

Although, if you are using Qt, you shouldn't be joining paths as strings.

See How to build a full path string (safely) from separate strings?

edited May 23, 2017 at 12:03

CommunityBot

11 silver badge

answered Jul 23, 2012 at 11:23

Liron

2,04219 silver badges39 bronze badges

3 Comments

Liron Over a year ago

Doh. Yeah, that would work too, so you have to make sure that all the strings above are QStrings. QString("\Data\") + QString(someReference) etc.

Bruce Over a year ago

QString has + operator so it would work. Except that if you got a null pointer, it crashes...

Bruce Over a year ago

@LKM : not necessarily, look at the prototypes in his link. Moreover, pobjects can be constructed on the flight by compiler to fit.

sara · Accepted Answer · 2012-07-23 12:50:10Z

-1

Thank you all for your answers.

It appears that I was wrong, and the segmentation fault was caused a line before, where I created the reference I mentioned in the question.

I discovered it with further debugging.

Sorry for the confusion, and thank you again!

answered Jul 23, 2012 at 12:50

sara

3,9449 gold badges46 silver badges75 bronze badges

Collectives™ on Stack Overflow

Qt - C++ string concatenation segmentation fault

3 Answers 3

2 Comments

3 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related