Empty an array of struct containing char*

Question

I have a struct which contains a set of char* properties.

struct gcp_values {
char* srcX;
char* srcY;
char* dstX;
char* dstY;
};

well I fill it in a loop from a set of qt objects

std::vector<GeoRefLibrary::gcp_values> gcpvalues(vl.size());

    for(int i=0;i<vl.size();i++) {
        gcppoint_ *a = qobject_cast<gcppoint_ *>(vl.at(i).value<QObject *>());
        gcpvalues[i].srcX= strdup(QString::number(a->row()).toStdString().c_str());
        gcpvalues[i].srcY= strdup(QString::number(a->column()).toStdString().c_str());
        gcpvalues[i].dstX= strdup(QString::number(a->lon()).toStdString().c_str());
        gcpvalues[i].dstY= strdup(QString::number(a->lat()).toStdString().c_str());
    }

when I run valgrind test it results these outpt

12 bytes in 4 blocks are definitely lost in loss record 813 of 19,623
14 bytes in 4 blocks are definitely lost in loss record 889 of 19,623
16 bytes in 1 blocks are definitely lost in loss record 3,621 of 19,623
32 bytes in 4 blocks are definitely lost in loss record 8,851 of 19,623
36 bytes in 4 blocks are definitely lost in loss record 9,134 of 19,623

these errors are at those lines in loop. I tried to delete [] gcpvalues but it returned wrong delete/free error. I searched and found this post too

delete[] an array of objects

but cant find the solutions,can some one please help me with this problem?

I also tried

    struct gcp_values {
    QString srcX;
    QString  srcY;
   QString  dstX;
    QString  dstY;
};

and it returns the same errors

---

I changed the loop into this and it seems errors are gone

for(int i=0;i<vl.size();i++) {
    gcppoint_ *a = qobject_cast<gcppoint_ *>(vl.at(i).value<QObject *>());

      char* srcX = strdup(QString::number(a->row()).toStdString().c_str());
      char* srcY = strdup(QString::number(a->column()).toStdString().c_str());
      char* dstX = strdup(QString::number(a->lon()).toStdString().c_str());
      char* dstY = strdup(QString::number(a->lat()).toStdString().c_str());
      gcpvalues[i].srcX=srcX;
      gcpvalues[i].srcY= srcY;
      gcpvalues[i].dstX= dstX;
      gcpvalues[i].dstY= dstY;
    if(srcX) { free(srcX);}
    if(srcY) { free(srcY);}
    if(dstX) { free(dstX);}
    if(dstY) { free(dstY);}
}

Answer 1

strdup is a POSIX function, and POSIX functions which allocate memory (and do not provide type-specific deallocation functions such as fclose and freeaddrinfo) expect the caller to eventually call free to deallocate the allocated memory.

POSIX does not use C++ memory allocation, so operator delete[] is not correct here.