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Gwyddion Library Reference Manual | ![]() |
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Top | Description |
#include <libgwyddion/gwyddion.h> #define GWY_EXPR_ERROR enum GwyExprError; GQuark gwy_expr_error_quark (void
); GwyExpr * gwy_expr_new (void
); void gwy_expr_free (GwyExpr *expr
); gboolean gwy_expr_evaluate (GwyExpr *expr
,const gchar *text
,gdouble *result
,GError **err
); gboolean gwy_expr_compile (GwyExpr *expr
,const gchar *text
,GError **err
); guint gwy_expr_resolve_variables (GwyExpr *expr
,guint n
,const gchar * const *names
,guint *indices
); gint gwy_expr_get_variables (GwyExpr *expr
,gchar ***names
); gdouble gwy_expr_execute (GwyExpr *expr
,const gdouble *values
); void gwy_expr_vector_execute (GwyExpr *expr
,guint n
,const gdouble **data
,gdouble *result
); gboolean gwy_expr_define_constant (GwyExpr *expr
,const gchar *name
,gdouble value
,GError **err
); gboolean gwy_expr_undefine_constant (GwyExpr *expr
,const gchar *name
); const gchar * gwy_expr_get_expression (GwyExpr *expr
); GwyExpr;
GwyExpr is an expression evaluator, more precisely parser, compiler, and
evaluator. A new GwyExpr can be created with gwy_expr_new()
, then it can be
used to evaluate any number of expressions; when it's no longer needed, it
should be destroyed with gwy_expr_free()
.
Expression syntax is described in Gwyddion user guide.
Simple arithmetic expressions without variables can be directly evaluated
with gwy_expr_evaluate()
.
Expression with variables have to be compiled first with gwy_expr_compile()
.
Then either gwy_expr_resolve_variables()
or gwy_expr_get_variables()
can be
used to obtain information what variables are present in the expression and
at which positions (variables are referenced by position, not name during
final evaluation because of effieiency reasons). Subsequent evaluation with
variable substitution is performed by gwy_expr_execute()
. It is also
possible to evaluate expression on each item of value arrays with
gwy_expr_vector_execute()
.
One-shot evaluation of expressions without variables is easy:
1 2 3 4 5 6 7 8 9 10 |
GwyExpr *expr; GError *err = NULL; gdouble result; expr = gwy_expr_new(); if (!gwy_expr_evaluate(expr, "1+2", &result, &err)) { /* Handle compilation error */ } g_print("The result: %g\n", result); gwy_expr_free(expr); |
One-shot evaluation of expressions with known variables can be performed by defining them as constants beforehand:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 |
GwyExpr *expr; GError *err = NULL; gdouble result; /* Create expression and define variables as constants */ expr = gwy_expr_new(); gwy_expr_define_constant(expr, "x", 3.0, NULL); gwy_expr_define_constant(expr, "y", 4.0, NULL); /* Evaluate expression */ if (!gwy_expr_evaluate(expr, "hypot x,y", &result, &err)) { /* Handle compilation error */ } g_print("The result: %g\n", result); gwy_expr_free(expr); |
When the same expression is evaluated multiple times with different
variable values and the variables are again from some known set, the
gwy_expr_resolve_variables()
should be used (if the repeated evaluation
happens over items of some arrays, gwy_expr_vector_execute()
is more
efficient and usually simplier to use too):
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 |
GwyExpr *expr; GError *err = NULL; const gchar *const var_names[] = { "lambda", "theta", "psi", "d", "k" }; const gdouble var_values1[] = { 300.0, 0.09, 2.0, 52.3, 1.43 }; const gdouble var_values2[] = { 400.0, 0.12, 2.0, 54.1, 1.44 }; guint var_positions[G_N_ELEMENTS(var_names)]; gdouble vars[G_N_ELEMENTS(var_names) + 1]; guint i; /* Create expression and define constant pi */ expr = gwy_expr_new(); gwy_expr_define_constant(expr, "pi", G_PI, NULL); /* Compile expression */ if (!gwy_expr_compile(expr, "2*pi/lambda*d*sin theta", &err)) { /* Handle compilation error */ } /* Resolve variables */ if (gwy_expr_resolve_variables(expr, G_N_ELEMENTS(var_names), var_names, var_positions)) { /* Expression contains unknown variables */ } /* Evaluate first set */ for (i = 0; i < G_N_ELEMENTS(var_names); i++) { vars[var_positions[i]] = var_values1[i]; } g_print("First result: %g\n", gwy_expr_execute(expr, vars)); /* Evaluate second set */ for (i = 0; i < G_N_ELEMENTS(var_names); i++) vars[var_positions[i]] = var_values2[i]; g_print("Second result: %g\n", gwy_expr_execute(expr, vars)); gwy_expr_free(expr); |
The most general case is when the variables are from a large set (or
completely arbitrary). Then it is best to get the list of variables with
gwy_expr_get_variables()
and supply only values of variables that
are actually present in the expression.
#define GWY_EXPR_ERROR gwy_expr_error_quark()
Error domain for expression parsing and evaluation. Errors in this domain will be from the GwyExprError enumeration. See GError for information on error domains.
typedef enum { GWY_EXPR_ERROR_CLOSING_PARENTHESIS, GWY_EXPR_ERROR_EMPTY, GWY_EXPR_ERROR_EMPTY_PARENTHESES, GWY_EXPR_ERROR_GARBAGE, GWY_EXPR_ERROR_INVALID_ARGUMENT, GWY_EXPR_ERROR_INVALID_TOKEN, GWY_EXPR_ERROR_MISSING_ARGUMENT, GWY_EXPR_ERROR_NOT_EXECUTABLE, GWY_EXPR_ERROR_OPENING_PARENTHESIS, GWY_EXPR_ERROR_STRAY_COMMA, GWY_EXPR_ERROR_UNRESOLVED_IDENTIFIERS, GWY_EXPR_ERROR_CONSTANT_NAME } GwyExprError;
Error codes returned by expression parsing and execution.
A closing parenthesis is missing. | |
Expression is empty. | |
A parentheses pair contain nothing inside. | |
An symbol unexpectedly managed to survive. | |
Function or operator argument is not a value. | |
Expression contains an invalid token. | |
Function or operator arguments is missing. | |
Compiled stack is not executable. | |
An opening parenthesis is missing. | |
A comma at the start or end of list. | |
Expression contains unresolved identifiers. | |
Constant name is invalid. |
GQuark gwy_expr_error_quark (void
);
Returns error domain for expression parsin and evaluation.
See and use GWY_EXPR_ERROR
.
Returns : |
The error domain. |
GwyExpr * gwy_expr_new (void
);
Creates a new expression evaluator.
Returns : |
A newly created expression evaluator. |
void gwy_expr_free (GwyExpr *expr
);
Frees all memory used by an expression evaluator.
|
An expression evaluator. |
gboolean gwy_expr_evaluate (GwyExpr *expr
,const gchar *text
,gdouble *result
,GError **err
);
Evaulates an arithmetic expression.
|
An expression evaluator. |
|
String containing the expression to evaluate. |
|
Location to store result to. |
|
Location to store compilation or evaluation error to, or NULL .
Errors from GwyExprError domain can occur. |
Returns : |
TRUE on success, FALSE if evaluation failed. |
gboolean gwy_expr_compile (GwyExpr *expr
,const gchar *text
,GError **err
);
Compiles an expression for later execution.
This function is useful for expressions with variables. For normal
arithmetic expressions it's easier to use gwy_expr_evaluate()
.
|
An expression evaluator. |
|
String containing the expression to compile. |
|
Location to store compilation or evaluation error to, or NULL .
Errors from GwyExprError domain can occur. |
Returns : |
TRUE on success, FALSE if compilation failed. |
guint gwy_expr_resolve_variables (GwyExpr *expr
,guint n
,const gchar * const *names
,guint *indices
);
Finds positions of variables in an expression.
|
An expression evaluator. |
|
The length of names and indices arrays. |
|
List of variable names to get positions of. |
|
Array to store variable positions to. The positions are the same
as in gwy_expr_execute() . Variables not present in the expression
are assigned (reserved) position 0. This allows to safely
substitute values of all variables before execution wthout caring
which variables are actually present. |
Returns : |
The number of remaining, unresolved variables in expr . |
gint gwy_expr_get_variables (GwyExpr *expr
,gchar ***names
);
Get the number, names, and indices of unresolved identifiers in expr
.
It is an error to call this function after an unsuccessful compilation.
If you only care about variables from a prefedined set, that is if any
unknown variable is an error, it's easier to use
gwy_expr_resolve_variables()
.
The position of each variable in names
corresponds to the position of its
value in values
array in gwy_expr_execute()
call. Namely, the first item
in the array is always reserved and do not correspond to any variable.
|
An expression evaluator. |
|
Location to store pointer to array of variable names to (may be
NULL to get just number of variables). The string array returned
in this argument in owned by expr and is valid only until next
gwy_expr_compile() , gwy_expr_evaluate() , or gwy_expr_free()
call. |
Returns : |
The length of array stored to names . This is the number of
variables plus one (for the first reserved item).
On failure, 0 is returned. |
gdouble gwy_expr_execute (GwyExpr *expr
,const gdouble *values
);
Executes a compiled expression with variables, substituting given values.
|
An expression evaluator. |
|
Array with variable values. Its zeroth item is always unused.
Variable list can be obtained by gwy_expr_get_variables() . |
Returns : |
The result. |
void gwy_expr_vector_execute (GwyExpr *expr
,guint n
,const gdouble **data
,gdouble *result
);
Executes a compiled expression on each item of data arrays.
|
An expression evaluator. |
|
The lenght of result and of data member arrays, that is vector length. |
|
An array of arrays of length n . The arrays correspond to expression
variables in gwy_expr_execute() . Zeroth array can be NULL . |
|
An array of length n to store computation results to. It may be
one of those in data . |
gboolean gwy_expr_define_constant (GwyExpr *expr
,const gchar *name
,gdouble value
,GError **err
);
Defines a symbolic constant.
Note the definition does not affect already compiled expression, you have to recompile it (and eventually re-resolve variables).
|
An expression evaluator. |
|
Name of constant to define. |
|
Constant numeric value. |
|
Location to store error to, or NULL .
Only GWY_EXPR_ERROR_CONSTANT_NAME error from GwyExprError domain can
occur. |
Returns : |
TRUE on success, FALSE if definition failed. |
gboolean gwy_expr_undefine_constant (GwyExpr *expr
,const gchar *name
);
Undefines a symbolic constant.
Note the definition removal does not affect already compiled expression, you have to recompile it (and eventually re-resolve variables).
const gchar * gwy_expr_get_expression (GwyExpr *expr
);
Gets the expression string.
|
An expression evaluator. |
Returns : |
The last string passed to gwy_expr_evaluate() or
gwy_expr_compile() . It is owned by expr and must not be modified
or freed. |
typedef struct _GwyExpr GwyExpr;
GwyExpr is an opaque data structure and should be only manipulated with the functions below.