warning: implicit declaration of function "pread"

Hi, While compiling my C program, I am getting warning as "warning: implicit declaration of function pread". I have included unistd.h header file(which contains pread function declaration). I also tried adding macro _XOPEN_SOURCE before including unistd.h header file, as it was suggested in one of the posts, but still I am getting the same warning. I tried to find answers on google, but I was unable to resolve it. Though I am getting correct result even with warning, I want to rectify it. Any help is appreciated. Thanks in advance. -Pooja.

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