Bytes' order with different C++ compilers

Sorry, I've got a question closely connected with this topic. Where
could I find the direct instruction that C++ compiler is not allowed
to manilupate the bytes' oreder in representation of numbers for its
free will. It could seem obivous for someone but not for me. I mean I
want be shure that on the same hardware platform different C++
comilers will expose the same bytes' order (if the platform itself
operates with fixed bytes' order of course).

Thank you in advance.

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