PostgreSQL Source Code  git master
unsetenv.c File Reference
#include "c.h"
Include dependency graph for unsetenv.c:

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Functions

int unsetenv (const char *name)
 

Function Documentation

◆ unsetenv()

int unsetenv ( const char *  name)

Definition at line 20 of file unsetenv.c.

References malloc, putenv, and sprintf.

21 {
22  char *envstr;
23 
24  /* Error conditions, per POSIX */
25  if (name == NULL || name[0] == '\0' || strchr(name, '=') != NULL)
26  {
27  errno = EINVAL;
28  return -1;
29  }
30 
31  if (getenv(name) == NULL)
32  return 0; /* no work */
33 
34  /*
35  * The technique embodied here works if libc follows the Single Unix Spec
36  * and actually uses the storage passed to putenv() to hold the environ
37  * entry. When we clobber the entry in the second step we are ensuring
38  * that we zap the actual environ member. However, there are some libc
39  * implementations (notably recent BSDs) that do not obey SUS but copy the
40  * presented string. This method fails on such platforms. Hopefully all
41  * such platforms have unsetenv() and thus won't be using this hack. See:
42  * http://www.greenend.org.uk/rjk/2008/putenv.html
43  *
44  * Note that repeatedly setting and unsetting a var using this code will
45  * leak memory.
46  */
47 
48  envstr = (char *) malloc(strlen(name) + 2);
49  if (!envstr) /* not much we can do if no memory */
50  return -1;
51 
52  /* Override the existing setting by forcibly defining the var */
53  sprintf(envstr, "%s=", name);
54  if (putenv(envstr))
55  return -1;
56 
57  /* Now we can clobber the variable definition this way: */
58  strcpy(envstr, "=");
59 
60  /*
61  * This last putenv cleans up if we have multiple zero-length names as a
62  * result of unsetting multiple things.
63  */
64  return putenv(envstr);
65 }
#define malloc(a)
Definition: header.h:50
#define sprintf
Definition: port.h:218
#define putenv(x)
Definition: win32_port.h:496
const char * name
Definition: encode.c:515