Your syntax is incorrect. It should be:

Qt Code: 
  1. connect(comboBox_Aaccount, &comboBox_Aaccount::activated, this, &whateverClassThisIs::selectAccount);
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The SIGNAL() and SLOT() macros of the old style were passed char * strings, which the Qt metatype system used to look up the actual function. The new style uses the address of the member function (signal or slot). Function addresses don't include the names / types of arguments.

In the connect statement I posted above, unless you have a member variable named "comboBox_Aaccount", this code won't compile either. The first argument to the connect() statement must be the name of the member variable that has the same type (or is derived from) the class used in the second argument. Likewise for the 3rd / 4th argument pair.