【C语言】编写函数实现库函数atof

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//编写函数实现库函数atof
#include <stdio.h>
#include <assert.h>
#include <ctype.h>
#include <math.h>
double calculate(const char *src, int flag)
{
	double num = 0.0;
	int n = 0;
	int count = 0;
	while (*src)
	{
		if ((*src >= '0') && (*src <= '9'))//判断输?入是否为?非数组字符
		{
			num = num * 10 + (*src - '0');
			src++;
			if (n)
			{
				count++;
			}
		}
		else if (*src == '.')
		{
			n = 1;
			src++;
		}
		else
		{
			num = 0;
			break;
		}
	}
	if (n)
	{
		num = num / powl(10,count);
	}
	return flag * num;
}
double str_to_int(const char *str)
{
	double num = 0.0;
	int flag = 1;
	if (str != NULL && *str != '\0')
	{
		while (isspace(*str))
		{
			str++;
		}
		if (*str == '+')
			str++;
		else if (*str == '-')
		{
			str++;
			flag = -1;
		}
		 if (*str != '\0')
		{
			num = calculate(str, flag);
		}
	}
	return num;
}
int main()
{
	printf("%f\n", str_to_int(" +23.45"));
	printf("%f\n", str_to_int(" -2.345"));
	printf("%f\n", str_to_int("+234.5"));
	printf("%f\n", str_to_int("-2345.44"));
	printf("%f\n", str_to_int("2345"));
	printf("%f\n", str_to_int("-1111.11"));
	printf("%f\n", str_to_int(""));
	printf("%f\n", str_to_int("123ab"));
	return 0;
}

【C语言】编写函数实现库函数atof

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原文地址：http://blog.csdn.net/doudouwa1234/article/details/46761883