_EDC_BYTE_SEEK

Indicates to z/OS® XL C/C++ that, for all binary files, ftell() should return relative byte offsets, and fseek() should use relative byte offsets as input. The default behavior is for only binary files with a fixed record format to support relative byte offsets. _EDC_BYTE_SEEK is set with the command:
setenv("_EDC_BYTE_SEEK","Y",1);