//  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;

}

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