58 lines
1.6 KiB
C
58 lines
1.6 KiB
C
/*-------------------------------------------------------------------------
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*
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* unsetenv.c
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* unsetenv() emulation for machines without it
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*
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* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/port/unsetenv.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "c.h"
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void
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unsetenv(const char *name)
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{
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char *envstr;
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if (getenv(name) == NULL)
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return; /* no work */
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/*
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* The technique embodied here works if libc follows the Single Unix Spec
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* and actually uses the storage passed to putenv() to hold the environ
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* entry. When we clobber the entry in the second step we are ensuring
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* that we zap the actual environ member. However, there are some libc
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* implementations (notably recent BSDs) that do not obey SUS but copy the
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* presented string. This method fails on such platforms. Hopefully all
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* such platforms have unsetenv() and thus won't be using this hack. See:
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* http://www.greenend.org.uk/rjk/2008/putenv.html
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*
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* Note that repeatedly setting and unsetting a var using this code will
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* leak memory.
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*/
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envstr = (char *) malloc(strlen(name) + 2);
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if (!envstr) /* not much we can do if no memory */
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return;
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/* Override the existing setting by forcibly defining the var */
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sprintf(envstr, "%s=", name);
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putenv(envstr);
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/* Now we can clobber the variable definition this way: */
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strcpy(envstr, "=");
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/*
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* This last putenv cleans up if we have multiple zero-length names as a
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* result of unsetting multiple things.
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*/
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putenv(envstr);
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}
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