String constructor of constant char* changes value of constant char*?

Question

The Current Issue

The value of a const char* seems to be changing to a nonsensical value.

Faulty Code Example

The intention of the code below is to create a string with the value of basedir . This process should keep the value of basedir constant; however, it inexplicably changes.

ProcessInfo get_process(int pid, const char* basedir) {
 cout<<basedir<<endl; 
 string basedir_str=basedir;
 cout<<basedir<<endl; 
 ....}

Current Output

./proc/16224/task
▒▒v▒=+

What could be wrong with the const char* to string assignment?

How Basedir Is Set

The variable basedir is being allocated with a call to the "parent" function get_all_processes.

Parent Function

vector<ProcessInfo> get_all_processes(const char* basedir) {
 DIR* dir;
 struct dirent *entry;
 vector<ProcessInfo> totalProcesses;
 //check to see if basedir can be opened
 if((dir =opendir(basedir))!=NULL){

    while((entry = readdir(dir)) != NULL ){
        int pid = atoi (entry->d_name);
        if(pid <=0){
            continue;
        }
        else{

        ProcessInfo currentProcess = get_process(pid, basedir); //<--call to get_process

        totalProcesses.push_back(currentProcess);
        }
    }
    closedir(dir);
}


return totalProcesses;
}

Call to Parent Function

myProcessInfo.threads=get_all_processes(threadList_fileName);
//threadList_filename='./proc/[pid]/task', in this case pid =16224

Solution

Eliminating the temporary const char* threadList_fileName and changing the arguments of the get_all_processes function. myProcessInfo.threads=get_all_processes(("./proc/"+pid_str+"/task").c_str());

Answer 1

It looks like the variable "basedir" already points to memory you do not own anymore. Just by coincidence it still holds the value that you assigned to it. By allocating memory for the string "basedir_str" this memory is reused and overwritten by other data. So your problem lies outside the of the function "get_process".

How do you allocate "basedir"?