def check_string(result, func, cargs, offset=-1, str_result=False):
"""
Checks the string output returned from the given function, and frees
the string pointer allocated by OGR. The `str_result` keyword
may be used when the result is the string pointer, otherwise
the OGR error code is assumed. The `offset` keyword may be used
to extract the string pointer passed in by-reference at the given
slice offset in the function arguments.
"""
if str_result:
# For routines that return a string.
ptr = result
if not ptr:
s = None
else:
s = string_at(result)
else:
# Error-code return specified.
check_err(result)
ptr = ptr_byref(cargs, offset)
# Getting the string value
s = ptr.value
# Correctly freeing the allocated memory behind GDAL pointer
# with the VSIFree routine.
if ptr:
lgdal.VSIFree(ptr)
return s
# ### DataSource, Layer error-checking ###
# ### Envelope checking ###
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