QStringList object unavalable in for loop

rcx11

I'm attempting to make a fake **argv[] and argc set to use with Boost Program Options. A line is read from a script file, and I'm using Program Options to parse it. As it is now, I'm reading the line from file successfully into a QString, and I'm splitting into a QStringList, apparently also successfully. I then try to make a C-style char * array. After reading the second string into the array, the QStringList is shown as unavailable, and I SEGFAULT when trying to execute the third loop.

The line being read (AppName substituted):

AppName -b black -c white -t $''

My code:

//Simulate argv** and argc
QStringList Qargv = line.split(' ', Qt::KeepEmptyParts);
int fargc = Qargv.count();      // Fake argc
char* fargv[fargc];     // Fake argv
for (int j = 0; j < fargc; j++)
     strcpy(fargv[j], Qargv.at(j).toStdString().c_str());

I've also tried Qargv.at(j).toLocal8bit().constData() with the same results. I've also attempted to move the declaration of Qargv up a scope, copy the C-string to an intermediate char * variable before assignment, and copying to a std::string to convert to C-string. Some results have been interesting, but this is the most succinct and easy to describe. It always goes <not available> after copying "-b" into fargv[1].

ChrisW67

You have not allocated memory to copy to the data at this address Qargv.at(j).toStdString().c_str() into. In your code each fargv[j] is uninitialized. Each fargv pointer should point to a block of memory that is large enough to hold the argument plus a \0 byte.

Depending on the data lifetime requirements and whether Boost program options modifies the data (I suspect not), there is possibly a neater way to do this using a QByteArray. Load the line into a QByteArray, swap the spaces/delimiters for \0, and build fargv with pointers into that buffer.

rcx11

Thanks for the help. I haven't messed with memory allocation much, so I didn't think about it. The code has been adjusted.

//Simulate argv** and argc
QStringList Qargv = line.split(' ', Qt::KeepEmptyParts);
int fargc = Qargv.count();      // Fake argc
char **fargv = new char*[fargc];     // Fake **argv.
for (int j = 0; j < fargc; j++)
   fargv[j] = qstrdup(Qargv.at(j).toStdString().c_str());

It now does mostly what I want it to do. What I have to figure out now is how to break up that QStringList so that I can keep all parts within $' ... ' together.

JonB

@rcx11 said in QStringList object unavalable in for loop:

I can keep all parts within $' ... ' together.

In that case splitting on space may not be what you intend. Show an example of what the complete string line looks like (I assume not just with the $'' empty at the end, else what is the problem?) and how you would want it to be split into separate arguments.

rcx11

I fiddled around and got it working.

QStringList preserveReminder;
QStringList Qargv;
if (line.contains("$\'"))
{
   preserveReminder = line.split("$\'", Qt::SkipEmptyParts);   // Split the reminder from the rest because I need to prserve it as a single string
   Qargv = preserveReminder.at(0).split(' ', Qt::SkipEmptyParts); // Split everything else into separate strings.
   Qargv.append("$\'" + preserveReminder.at(1));   // Add the second string back with a restored $'
}
else
   Qargv = line.split(' ', Qt::SkipEmptyParts);

The nature of what I'm writing, I don't have to worry about multiple $' .. .' segments.