A few years ago I programmed AVR ATmega8 with AVR studio by USB isp programmer. I was using C language. Now I would like to use arduino(C++) langauge and my external USB isp programmer. Is it possible?
The Arduino IDE compiles and outputs standard Intel HEX format files that are compatible with (nearly?) all programmers. If you enable detailed logging in the preferences panel you can find out which directory the IDE is building your code in and if the IDE does not include specific support for your programmer you can then locate the .hex file and upload it using the tool you are familiar with. The projects are typically built in a
build.* subdirectory under %TEMP% (or /tmp on unix).
If you want to use arduino IDE to program the atmega328 you don't need a USB ISP programmer. The only thing you have to do is load the arduino bootloader on the atmega328 in order to program it through the arduino IDE. In the ide you can program the board with c++. But if you want to program the atmega328 through you're USB ISP programmer (assuming it is capable of programming the Atmega 328) you have to use other IDE in which you can program in c++ and produce an hex file that can be burned on the chip through you're programmer on the atmega328.