CODEWITHSUNDEEP
c++cpointersstring
Marcos Vasconcelos
Marcos Vasconcelos

Reputation: 18276

char* losing data

I'm writing a C++ code with returns some data, the problem is: my const char is losing it value each time I call it from another file. I don't have idea what's happening.

My code on ProcClient.h

virtual void reportWorkflowError(unsigned int workflow,
        const dp::String& errorCode) {
    char message[1000];
    snprintf(message, 1000, "Workflow: %s ERROR: %s", workflowToString(
            workflow).utf8(), errorCode.utf8());
    printf("[%s]", message);

    errorInfo = message;
}
virtual const char * getErrorInfo() {
    return errorInfo;
}

[Workflow: DW_FULFILL ERROR: E_ADEPT_NO_TOKEN]

[Workflow: ERROR: E_ADEPT_NOT_READY]

//two errors was thrown, and the errorInfo should has the last

On Services.cpp I start a "workflow", and if it throws an error the listener above is called, and after that I should get tha lastError pointer.

//g_drmClient is the ProcClient

bool RMServices::startFullfilment(dp::String acsm) {
    //Do things 
g_drmClient->getProcessor()->startWorkflows(dpdrm::DW_FULFILL);
size_t count = g_drmClient->getProcessor()->getFulfillmentItems();
printf("Number of items fulfilled: %d\n", count);

bool returnValue = !g_drmClient->hasError();
if (!returnValue)
    lastError = g_drmClient->getErrorInfo());

printf("[%s]", lastError);

return returnValue;
}

Here it prints: [\æ¾°Ô¯£ ¯|æ¾\æ¾er of items fulfer of ite]

What's happening?

Upvotes: 1

Views: 1811

Answers (3)

geekosaur
geekosaur

Reputation: 61457

You're putting message on the stack. Maybe you want it to be static, or better an instance variable.

Upvotes: 1

Mahesh
Mahesh

Reputation: 34655

char message[1000];

is a local variable residing on stack and goes out of scope on return of reportWorkflowError. So, 

errorInfo = message; // errorInfo is simply pointing to garbage on method return.

Do some thing on these lines -

void className::foo()
{
    char stackVariable[] = "abcdef" ;
    classVariableCharPointer = new char[ sizeof(stackVariable) + 1 ] ;

    strcpy( classVariableCharPointer, stackVariable ) ;
}

Also remember to deallocate the classVariableCharPointer in the destructor using delete[].

Upvotes: 8

Jonathan Wood
Jonathan Wood

Reputation: 67345

Yikes, you can't do that.

As soon as reportWorkflowError returns, all local variables are destroyed. This includes message, which returnValue points to.

A better approach would include making returnValue a character array, and calling srtrcpy() to copy the local data to the member variable. This way, the copy would still exist after message is destroyed.

Upvotes: 2

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