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variables.h
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1 /*
2  * psql - the PostgreSQL interactive terminal
3  *
4  * Copyright (c) 2000-2017, PostgreSQL Global Development Group
5  *
6  * This implements a sort of variable repository. One could also think of it
7  * as a cheap version of an associative array. Each variable has a string
8  * name and a string value. The value can't be NULL, or more precisely
9  * that's not distinguishable from the variable being unset.
10  *
11  * src/bin/psql/variables.h
12  */
13 #ifndef VARIABLES_H
14 #define VARIABLES_H
15 
16 /*
17  * Variables can be given "assign hook" functions. The assign hook can
18  * prevent invalid values from being assigned, and can update internal C
19  * variables to keep them in sync with the variable's current value.
20  *
21  * An assign hook function is called before any attempted assignment, with the
22  * proposed new value of the variable (or with NULL, if an \unset is being
23  * attempted). If it returns false, the assignment doesn't occur --- it
24  * should print an error message with psql_error() to tell the user why.
25  *
26  * When an assign hook function is installed with SetVariableHooks(), it is
27  * called with the variable's current value (or with NULL, if it wasn't set
28  * yet). But its return value is ignored in this case. The hook should be
29  * set before any possibly-invalid value can be assigned.
30  */
31 typedef bool (*VariableAssignHook) (const char *newval);
32 
33 /*
34  * Variables can also be given "substitute hook" functions. The substitute
35  * hook can replace values (including NULL) with other values, allowing
36  * normalization of variable contents. For example, for a boolean variable,
37  * we wish to interpret "\unset FOO" as "\set FOO off", and we can do that
38  * by installing a substitute hook. (We can use the same substitute hook
39  * for all bool or nearly-bool variables, which is why this responsibility
40  * isn't part of the assign hook.)
41  *
42  * The substitute hook is called before any attempted assignment, and before
43  * the assign hook if any, passing the proposed new value of the variable as a
44  * malloc'd string (or NULL, if an \unset is being attempted). It can return
45  * the same value, or a different malloc'd string, or modify the string
46  * in-place. It should free the passed-in value if it's not returning it.
47  * The substitute hook generally should not complain about erroneous values;
48  * that's a job for the assign hook.
49  *
50  * When a substitute hook is installed with SetVariableHooks(), it is applied
51  * to the variable's current value (typically NULL, if it wasn't set yet).
52  * That also happens before applying the assign hook.
53  */
54 typedef char *(*VariableSubstituteHook) (char *newval);
55 
56 /*
57  * Data structure representing one variable.
58  *
59  * Note: if value == NULL then the variable is logically unset, but we are
60  * keeping the struct around so as not to forget about its hook function(s).
61  */
62 struct _variable
63 {
64  char *name;
65  char *value;
68  struct _variable *next;
69 };
70 
71 /* Data structure representing a set of variables */
72 typedef struct _variable *VariableSpace;
73 
74 
75 VariableSpace CreateVariableSpace(void);
76 const char *GetVariable(VariableSpace space, const char *name);
77 
78 bool ParseVariableBool(const char *value, const char *name,
79  bool *result);
80 
81 bool ParseVariableNum(const char *value, const char *name,
82  int *result);
83 
84 void PrintVariables(VariableSpace space);
85 
86 bool SetVariable(VariableSpace space, const char *name, const char *value);
87 bool SetVariableBool(VariableSpace space, const char *name);
88 bool DeleteVariable(VariableSpace space, const char *name);
89 
90 void SetVariableHooks(VariableSpace space, const char *name,
92  VariableAssignHook ahook);
93 
94 void PsqlVarEnumError(const char *name, const char *value, const char *suggestions);
95 
96 #endif /* VARIABLES_H */
void PrintVariables(VariableSpace space)
Definition: variables.c:186
struct _variable * VariableSpace
Definition: variables.h:72
char *(* VariableSubstituteHook)(char *newval)
Definition: variables.h:54
bool DeleteVariable(VariableSpace space, const char *name)
Definition: variables.c:379
VariableSpace CreateVariableSpace(void)
Definition: variables.c:51
char bool
Definition: c.h:257
bool(* VariableAssignHook)(const char *newval)
Definition: variables.h:31
bool ParseVariableBool(const char *value, const char *name, bool *result)
Definition: variables.c:107
VariableAssignHook assign_hook
Definition: variables.h:67
struct _variable * next
Definition: variables.h:68
void PsqlVarEnumError(const char *name, const char *value, const char *suggestions)
Definition: variables.c:391
char * name
Definition: variables.h:64
const char * GetVariable(VariableSpace space, const char *name)
Definition: variables.c:71
#define newval
bool SetVariable(VariableSpace space, const char *name, const char *value)
Definition: variables.c:211
VariableSubstituteHook substitute_hook
Definition: variables.h:66
bool SetVariableBool(VariableSpace space, const char *name)
Definition: variables.c:367
void SetVariableHooks(VariableSpace space, const char *name, VariableSubstituteHook shook, VariableAssignHook ahook)
Definition: variables.c:315
char * value
Definition: variables.h:65
bool ParseVariableNum(const char *value, const char *name, int *result)
Definition: variables.c:156