expression.c File Reference

A compact math expression engine. More...

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "types.h"
#include "errors.h"
#include "symbolic.h"
#include "expression.h"

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Functions
expression_t	expression_new (void)
	New blank expression. More...
expression_t	expression_new_value (value_t val)
expression_t	expression_new_tree (char op, expression_t left, expression_t right)
expression_t	expression_new_sym (sym_t sym)
void	expression_free (expression_t exp)
	Free an expression. More...
value_t	expression_evaluate (expression_t exp)
void	expression_to_string (char *dst_str, expression_t src_exp)
	Expression to String. More...
size_t	number_len (size_t str_len, char *str)
void	str_cpy (char *dest, const char *src, size_t count)
	Same as strncpy, but throws an error if a null character is reached in src. More...
expression_t	string_to_expression (size_t str_len, char const *str)
	Convert String to an Expression. More...

Detailed Description

A compact math expression engine.

Date

Apr 6, 2014

Author

Craig Hesling

Function Documentation

expression_evaluate()

value_t expression_evaluate

(

expression_t

exp

)

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expression_free()

void expression_free

(

expression_t

exp

)

Free an expression.

Parameters

exp	The expression to free

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expression_new()

expression_t expression_new

(

void

)

New blank expression.

This function creates the most basic empty expression.

Returns

A new empty expression

expression_new_sym()

expression_t expression_new_sym

(

sym_t

sym

)

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expression_new_tree()

expression_t expression_new_tree	(	char	op,
		expression_t	left,
		expression_t	right
	)

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expression_new_value()

expression_t expression_new_value

(

value_t

val

)

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expression_to_string()

void expression_to_string	(	char *	dst_str,
		expression_t	src_exp
	)

Expression to String.

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number_len()

size_t number_len	(	size_t	str_len,
		char *	str
	)

str_cpy()

void str_cpy	(	char *	dest,
		const char *	src,
		size_t	count
	)

Same as strncpy, but throws an error if a null character is reached in src.

Parameters

dest	Destination string buffer.
src	Source string buffer.
count	The number of bytes to copy.

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string_to_expression()

expression_t string_to_expression	(	size_t	str_len,
		char const *	str
	)

Convert String to an Expression.

Parses a string into an expression.

Note

level was type int - changed to unsigned to temporarily quiet compiler

Bug:

Cannot parse negative numbers

Warning

Symbols must start with ALPHA chars to be properly identified.

Algorithm

Parsing Overview

• Step 1: Recording details about the string while scanning from left to right.
• Step 2: There are two real cases. The string is a single number (with no operations) or it is two sub-expressions joined by an operation.
  Cases:
  • If it is a simple number, we know how to parse it and create a value expression.
  • If it is not just a number, we want split the string about the operation at the lowest level. (in practice, we end up finding the one that is farthest left of the lowest level) We then construct a tree expression with the chosen operation and the sub-expression results from running the function recursively on each of the sub-strings.

Parameters

str_len	Length of given string
str	String to parse

Returns

The expression_t representation of the inputed string

Test:

Test for negative values

Todo:

Allow symbols to be detected when they start with numeric digits also. string_to_sym is already compatible.

< Store original index

< Used to explore the presence of a symbol parameter

Todo:

Do series of additional syntax checks here.

Todo:

Syntax Check: Check that level==0

Todo:

Syntax Check: Check that oparen_count==cparen_count

Note

left_buf and right_buf were changed to use malloc to avoid errors with C90 compilers

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