【c语言】模拟实现库函数的atof函数

//  模拟实现库函数的atof函数

#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <ctype.h>

double my_atof(char const *p)
{
	double ret = 0;
	int flag = 1;
	int count = 0;
	assert(p != NULL);
	while (isspace(*p))
	{
		p++;
	}
	while (*p)
	{
		if (count)
		{
			count = count * 10;
		}
		if (*p == '+')
			p++;
		else if (*p == '-')
		{
			p++;
			flag = -1;
		}
		else if (*p == '.')
		{
			count++;
			p++;
		}
		else if (*p >= '0'&& *p <= '9')
		{
			ret = ret * 10 + (*p - '0');
			p++;
		}
		else
			return 0;
	}
	return ret*flag / count;
}

int main()
{
	printf("%f\n", my_atof(" +23.45"));
	printf("%f\n", my_atof(" -2.345"));
	printf("%f\n", my_atof("+234.5"));
	printf("%f\n", my_atof("-23.45"));
	printf("%f\n", my_atof("2.345"));
	printf("%f\n", my_atof("234.5"));
	printf("%f\n", my_atof(" ."));
	printf("%f\n", my_atof("12.3ab"));
	return 0;
}

<img src="http://img.blog.csdn.net/20150704160911903?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />