Undefined reference to XXXX

Help compile a thing today, prompt undefined reference to XXXX. This error is a linker error, for a long while, the only thing more like a clue is the library's dependency order.

Later saw someone say the link option two times, such as GCC ' pkg-config--cflags--libs gtk+-2.0 libusb-1.0 ' xx.c-o xx ' pkg-config--cflags--lib s gtk+-2.0 libusb-1.0 ', incredibly on the Magic Pass.

think there is a reason, if the link order is really related, then this is symmetric, in case there is a dependence on the reverse order, it will increase the direction of dependence, to avoid problems.

Undefined reference to XXXX