I have a problem with LibRaw(0.20.2, MSVC2012) using std::map

Here is the test code
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std::map test;
test["elem1"].imgdata.params.user_qual = 10;
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There is no compile error, but runtime error occurs at

"test["elem1"].imgdata.params.user_qual = 10;"

I don't know why std::vector is work well but std::map is NOT work well.....
Does anyone know how to fix this error?