Внешняя сортировка прямым слиянием

Здравствуйте! Помогите,пожалуйста, решить проблему! Написал алгоритм внешней сортировки прямым слиянием. Почему то, если использовать стандартный сишные функции работы с файлами он работает, но при использовании QFile нет.
Вот код:
#include <QFile>
#include <QTextStream>
#include <QMessageBox>
void straightSort (){
int a1, a2, k, i, j, n;
//FILE *mainFile, *subFile1, *subFile2;
QFile mainFile("file.csv"), subFile1("subFile1.csv"), subFile2("subFile2.csv");

n = 0;
// mainFile = fopen(name,"r");
mainFile.open(QIODevice::ReadOnly);
// while ( !feof(mainFile) ) {
while (!mainFile.atEnd()) {
//fscanf(mainFile,"%d",&a1);
mainFile.readLine();
n++;
}
//fclose(mainFile);
mainFile.close();
k = 1;
while ( k < n ){
//mainFile = fopen(name,"r");
mainFile.open(QIODevice::ReadOnly);
//subFile1 = fopen("smsort_1","w");
subFile1.open(QIODevice::WriteOnly);
//subFile2 = fopen("smsort_2","w");
subFile2.open(QIODevice::WriteOnly);
//if ( !feof(mainFile) ) fscanf(mainFile,"%d",&a1);
if (!mainFile.atEnd()){
QString str = mainFile.readLine();
a1 = str.toInt();
}
QMessageBox msgBox;
msgBox.setText(QString::number(a1));
msgBox.exec();

//while ( !feof(mainFile) ){
while (!mainFile.atEnd()){
// for ( i = 0; i < k && !feof(mainFile) ; i++ ){
for ( i = 0; i < k && !mainFile.atEnd() ; i++ ){
//fprintf(subFile1,"%d ",a1);
subFile1.write(QString::number(a1).toUtf8());
subFile1.write("\n");
//fscanf(mainFile,"%d",&a1);
QString str = mainFile.readLine();
a1 = str.toInt();
}
// for ( j = 0; j < k && !feof(mainFile) ; j++ ){
for ( j = 0; j < k && !mainFile.atEnd() ; j++ ){
//fprintf(subFile2,"%d ",a1);
subFile2.write(QString::number(a1).toUtf8());
subFile2.write("\n");
//fscanf(mainFile,"%d",&a1);
QString str = mainFile.readLine();
a1 = str.toInt();
}
}
//fclose(subFile2);
subFile2.close();
// fclose(subFile1);
subFile1.close();
//fclose(mainFile);
mainFile.close();

//mainFile = fopen(name,"w");
mainFile.open(QIODevice::WriteOnly);
//subFile1 = fopen("smsort_1","r");
subFile1.open(QIODevice::ReadOnly);
//subFile2 = fopen("smsort_2","r");
subFile2.open(QIODevice::ReadOnly);

//if ( !feof(subFile1) ) fscanf(subFile1,"%d",&a1);
if (!subFile1.atEnd()){
QString str = subFile1.readLine();
a1 = str.toInt();
}

//if ( !feof(subFile2) ) fscanf(subFile2,"%d",&a2);
if (!subFile2.atEnd()){
QString str = subFile2.readLine();
a2 = str.toInt();
}

// while ( !feof(subFile1) && !feof(subFile2) ){
while (!subFile1.atEnd() && !subFile2.atEnd()) {
i = 0; j = 0;
//while ( i < k && j < k && !feof(subFile1) && !feof(subFile2) ) {
while ( i < k && j < k && !subFile1.atEnd() && !subFile2.atEnd()) {

if ( a1 < a2 ) {
//fprintf(mainFile,"%d ",a1);
mainFile.write(QString::number(a1).toUtf8());
mainFile.write("\n");
//fscanf(subFile1,"%d",&a1);
QString str = subFile1.readLine();
a1 = str.toInt();
i++;
}
else {
//fprintf(mainFile,"%d ",a2);
mainFile.write(QString::number(a2).toUtf8());
mainFile.write("\n");
//fscanf(subFile2,"%d",&a2);
QString str = subFile2.readLine();
a2 = str.toInt();
j++;
}
}
//while ( i < k && !feof(subFile1) ) {
while ( i < k && !subFile1.atEnd() ) {
//fprintf(mainFile,"%d ",a1);
mainFile.write(QString::number(a1).toUtf8());
mainFile.write("\n");
//fscanf(subFile1,"%d",&a1);
QString str = subFile1.readLine();
a1 = str.toInt();
i++;
}
// while ( j < k && !feof(subFile2) ) {
while ( j < k && !subFile2.atEnd() ) {
// fprintf(mainFile,"%d ",a2);
mainFile.write(QString::number(a2).toUtf8());
mainFile.write("\n");
//fscanf(subFile2,"%d",&a2);
QString str = subFile2.readLine();
a2 = str.toInt();
j++;
}
}
//while ( !feof(subFile1) ) {
while (!subFile1.atEnd()) {
// fprintf(mainFile,"%d ",a1);
mainFile.write(QString::number(a1).toUtf8());
mainFile.write("\n");
//fscanf(subFile1,"%d",&a1);
QString str = subFile1.readLine();
a1 = str.toInt();
}
//while ( !feof(subFile2) ) {
while (!subFile2.atEnd()) {
//fprintf(mainFile,"%d ",a2);
mainFile.write(QString::number(a2).toUtf8());
mainFile.write("\n");
//fscanf(subFile2,"%d",&a2);
QString str = subFile2.readLine();
a2 = str.toInt();
}
subFile2.close();
subFile1.close();
mainFile.close();
k *= 2;
}
//subFile1.remove();
//subFile2.remove();
}