Use:
char QChar::toLatin1() const
From the doc:
Returns the Latin-1 character equivalent to the QChar, or 0. This is mainly useful for non-internationalized software.
From a Qt5.0 version
char QChar::toAscii() const
This function is deprecated. Returns the Latin-1 character value of the QChar, or 0 if the character is not representable.
Example
QString test("test");
QChar c = test.at(0);
int v_latin = c.toLatin1();
int v_ascii = c.toAscii();
qDebug() << v_latin << " " << v_ascii;
Output:
116 116