C语言字符串数字提取函数，支持负数、浮点数、科学记数法

平台：
STC89C52
Keil uVision V5.29.0.0
PK51 Prof.Developers Kit Version:9.60.0.0

---

效果

这里以51单片机为例，对串口接收的字符串中的第三个数进行解码：

普通数字

小数

科学记数法

源码

/*
* Str2Num.h
*
*  Created on: 2021/11/6
*      Author: 乙酸氧铍
*/

#ifndef STR2NUM_H_
#define STR2NUM_H_

#include "stdint.h"

/*
str:数字字符串首地址
flag:分隔符
no:第no个数字 从1开始计
Output: 输出结果
*/

extern void str2int(char * str, char flag, int32_t no, int32_t *Output);
extern void str2double(char * str, char flag, int32_t no, double *Output);

#endif /* STR2NUM_H_ */

/*
* Str2Num.c
*
*  Created on: 2021/11/6
*      Author: 乙酸氧铍
*/
#include "Str2Num.h"

void str2int(char * str, char flag, int32_t no, int32_t *Output)
{
    
    
	int32_t id_end, count, output;
	for (id_end = 0, count = 0; count != no; ++id_end)
	{
    
    
		if (str[id_end] == flag || str[id_end] == '\r' || str[id_end] == '\n' || str[id_end] == '\0')
			++count;
	}
	id_end -= 2;
	for (output = 0, count = 1; str[id_end] != flag && id_end >= 0; --id_end)
	{
    
     
		if (str[id_end] == '-')
			output *= -1;
		else if (str[id_end] == '+')
			;
		else 
		{
    
    
			output += (str[id_end] - '0') * count;
			count *= 10;
		}
	}
	*Output = output;
}

void str2double(char * str, char flag, int32_t no, double *Output)
{
    
    
	int32_t id_end, id_dot, id_e, count, id, pow;
	double output;
	for (id_end = 0, count = 0; count != no; ++id_end)
	{
    
    
		if (str[id_end] == flag || str[id_end] == '\r' || str[id_end] == '\n' || str[id_end] == '\0')
			++count;
	}
	id_end -= 2;	//寻找最后一个数字的下标

	for (id_dot = id_end, id_e = -1; str[id_dot] != '.'; --id_dot)
	{
    
    
		if (str[id_dot] == 'e' || str[id_dot] == 'E')
			id_e = id_dot;			//标记e的下标
		if (str[id_dot] == flag || str[id_dot] == '\r' || str[id_dot] == '\n' || str[id_dot] == '\0')
		{
    
    
			if(id_e > 0)
				id_dot = id_e;
			else
				id_dot = id_end + 1;	
			break;
		}
	}

	output = 0;
	if (str[id_dot] == '.')
	{
    
    
		for (count = 10, id = id_dot + 1; str[id] != flag && str[id] != '\r' && str[id] != '\n' && str[id] != '\0' && str[id] != 'e' && str[id] != 'E'; ++id)
		{
    
    
			output += (str[id] - '0') / (double)count;	//加入小数部分
			count *= 10;
		}
	}

	for (count = 1, id = id_dot - 1; str[id] != flag && id >= 0; --id)
	{
    
    
		if (str[id] == '-')
			output *= -1;
		else if (str[id] == '+')
			;
		else
		{
    
    
			output += (str[id] - '0') * count;
			count *= 10;								//加入整数部分
		}
	}

	if(id_e > 0)										//指数计算
	{
    
     
		for (pow = 0, count = 1; id_end != id_e; --id_end)
		{
    
    
			if (str[id_end] == '+')
				;
			else if (str[id_end] == '-')
				pow *= -1;
			else 
			{
    
     
				pow += (str[id_end] - '0') * count;
				count *= 10;
			}
		}
		if (pow > 0)
			while (pow--)
				output *= 10;
		else if(pow < 0)
			while (pow++)
				output /= 10;
	}
	*Output = output;
}