printf("%s,%s,%d\n",__FILE__,__func__,__LINE__);
12、二级指针的应用 1）改变指针的值
#include <stdio.h>
#include <stdlib.h>
int main()
{
int i = 9;
int* p = &i;
*p = 0xb;
//用指针改变一个变量的值
printf("i=0x%x\n",i);
printf("p=0x%x\n",p);
int** q = &p;
**q = 0xc;
//用二级指针改变一个变量的值
printf("i=0x%x\n",i);
printf("p=0x%x\n",p);
*q = (int *)0xFFFFFFFF;
//用二级指针改变一个指针的值
printf("i=0x%x\n",i);
printf("p=0x%x\n",p);
return 0;
}
2）用函数来改变指针的值
# include <stdio.h>
void f(int ** q);
int main(void)
{
int i = 9;
int * p = &i;
printf("p=0x%x\n", p);
f(&p);
printf("p=0x%x\n", p);
return 0;
}
void f(int ** q)
{
*q = (int *)0xFFFFFFFF;
}
11、CRC
#include "stdio.h"
#include "stdint.h"
uint16_t CRC_calc(uint8_t *start, uint8_t *end)
{
uint16_t crc = 0x0;
uint8_t *data;
for (data = start; data < end; data++)
{
crc = (crc >> 8) | (crc << 8);
crc ^= *data;
crc ^= (crc & 0xff) >> 4;
crc ^= crc << 12;
crc ^= (crc & 0xff) << 5;
}
return crc;
}
//计算CRC的地址从start--->end+1
int main(void)
{
uint8_t a[7]={0x00,0x06,0x00,0x00,0x00,0xa0,0x00};
uint8_t c[7]={0x2b,0x06,0x00,0x00,0x00,0xa0,0x00};
uint16_t b=CRC_calc(&a[0],&a[6]);
//uint16_t b=CRC_calc(&c[0],&c[6]);
printf("b=0x%x\r\n",b);
}
10、清除数组为0的项
#include <stdio.h>
#include <stdint.h>
uint8_t a[10]={1,2,3,4,5,6,7,8,9,0};
static uint8_t delete_zero_item(uint8_t data[] , uint8_t n)
{
uint8_t i = 0, j, len = n;
while (i < len){
if( (data[i] == 0) ){
for (j = i; j < len; j++){
data[j] = data[j + 1];
}
len--;
}
else
i++;
}
return len;
}
int main(void)
{
uint8_t k=delete_zero_item(a,10);
printf("%d\n",k);
for(int i=0;i<k;i++) printf("%d",a[i]);
}
9、简易abs函数功能实现（求无符号整形表达式的绝对值） 无符号整形数据的差值，不能用if来判断，加一个常数截在一个区间。
#include "stdio.h"
#include "stdint.h"
#define ABS(x) (x>0?x:-(x))
int main()
{
uint32_t utc_time_tmp = 11;
uint32_t utc_time_r = 5;
if(utc_time_tmp - utc_time_r + 5 > 10)
//也是够了
//if(ABS(utc_time_tmp - utc_time_r)>5)
//也是够了
//if(((utc_time_tmp > utc_time_r) && (utc_time_tmp - utc_time_r > 5))||
// ((utc_time_tmp < utc_time_r) && (utc_time_r - utc_time_tmp > 5))
//)
printf("in\r\n");
else printf("out\r\n");
return 0;
}
8、在字符串中截取字符/字符串（GPS NMEA协议解析）
#include<stdio.h>
#include<string.h>
#include <stdlib.h>
#include <stdio.h>
int main(){
char* str = "123,456,789,0123456,123456,0,09,10";
char sub[3];
int count = 0, index = 0;
for (index = 0; index < strlen(str); ++index){
if (str[index] == ',')
++count;
if (count == 6)
break;
}
strncpy(sub, &str[index+1], 2);
sub[2] = '\0';
printf(sub); //123,456,789
int n = atoi(sub);
printf("string = %s integer = %d\n", sub, n);
}
7、sqrt的实现
#include <stdio.h>
#ifdef CONFIG_64BIT
#define BITS_PER_LONG 64
#else
#define BITS_PER_LONG 32
#endif
/**
* int_sqrt - rough approximation to sqrt
* @x: integer of which to calculate the sqrt
*
* A very rough approximation to the sqrt() function.
*/
unsigned long int_sqrt(unsigned long x)
{
unsigned long op, res, one;
op = x;
res = 0;
one = 1UL << (BITS_PER_LONG - 2);
while (one > op)
one >>= 2;
while (one != 0) {
if (op >= res + one) {
op = op - (res + one);
res = res + 2 * one;
}
res /= 2;
one /= 4;
}
return res;
}
int main(void)
{
printf("%d\n",int_sqrt(16)) ;
return 0 ;
}
6、数据转换(hex - char - byte array - acsii)
网上的整理过来的，来源记不清了，感谢作者。
DataConvert.c
#include <stdio.h>
#include <string.h>
#include "DataConvert.h"
int strToHex(char *ch, char *hex)
{
int high,low;
int tmp = 0;
if(ch == NULL || hex == NULL){
return -1;
}
if(strlen(ch) == 0){
return -2;
}
while(*ch){
tmp = (int)*ch;
high = tmp >> 4;
low = tmp & 15;
*hex++ = valueToHexCh(high); //先写高字节
*hex++ = valueToHexCh(low); //其次写低字节
ch++;
}
*hex = '\0';
return 0;
}
int hexToStr(char *hex, char *ch)
{
int high,low;
int tmp = 0;
if(hex == NULL || ch == NULL){
return -1;
}
if(strlen(hex) %2 == 1){
return -2;
}
while(*hex){
high = hexCharToValue(*hex);
if(high < 0){
*ch = '\0';
return -3;
}
hex++; //指针移动到下一个字符上
low = hexCharToValue(*hex);
if(low < 0){
*ch = '\0';
return -3;
}
tmp = (high << 4) + low;
*ch++ = (char)tmp;
hex++;
}
*ch = '\0';
return 0;
}
int hexCharToValue(const char ch){
int result = 0;
//获取16进制的高字节位数据
if(ch >= '0' && ch <= '9'){
result = (int)(ch - '0');
}
else if(ch >= 'a' && ch <= 'z'){
result = (int)(ch - 'a') + 10;
}
else if(ch >= 'A' && ch <= 'Z'){
result = (int)(ch - 'A') + 10;
}
else{
result = -1;
}
return result;
}
char valueToHexCh(const int value)
{
char result = '\0';
if(value >= 0 && value <= 9){
result = (char)(value + 48); //48为ascii编码的‘0’字符编码值
}
else if(value >= 10 && value <= 15){
result = (char)(value - 10 + 65); //减去10则找出其在16进制的偏移量，65为ascii的'A'的字符编码值
}
else{
;
}
return result;
}
int hexChartoByte(char *s,char *byte)
{
int i,n = 0;
for(i = 0; s[i]; i += 2)
{
if(s[i] >= 'A' && s[i] <= 'F')
byte[n] = s[i] - 'A' + 10;
else byte[n] = s[i] - '0';
if(s[i + 1] >= 'A' && s[i + 1] <= 'F')
byte[n] = (byte[n] << 4) | (s[i + 1] - 'A' + 10);
else byte[n] = (byte[n] << 4) | (s[i + 1] - '0');
++n;
}
return n;
}
unsigned char ChartoAscii(const unsigned char cha)
{
unsigned char ascii;
if ((cha >= 0x0A) && (cha <= 0x0F))
{
ascii = cha + 'A' - 10;
}
else
{
ascii = cha + '0';
}
return ascii;
}
DataConvert.h
#ifndef __DATA_H
#define __DATA_H
int strToHex(char *ch, char *hex);
int hexToStr(char *hex, char *ch);
int hexCharToValue(const char ch);
char valueToHexCh(const int value);
int hexChartoByte(char *s,char *byte);
unsigned char ChartoAscii(const unsigned char cha);
#endif
main.c
#include <stdio.h>
#include <string.h>
#include "DataConvert.h"
#define MCU_FIRWARE_VERSION "V1.0.0"
#define BLE_FIRWARE_VERSION "V1.0.0"
#define FONT_VERSION "V1.0.0"
int main(int argc, char *argv[])
{
int i;
char result[1024];
char *p_result = result;
//转换版本号数据
char mcu_version_hex[12];
char mcu_version_byte[6];
char *p_ch = MCU_FIRWARE_VERSION;
char *p_hex = mcu_version_hex;
strToHex(p_ch,p_hex);
int n = hexChartoByte(mcu_version_hex,mcu_version_byte);
char ble_version_hex[12];
char ble_version_byte[6];
p_ch = BLE_FIRWARE_VERSION;
p_hex = ble_version_hex;
strToHex(p_ch,p_hex);
int m = hexChartoByte(ble_version_hex,ble_version_byte);
char font_version_hex[12];
char font_version_byte[6];
p_ch = FONT_VERSION;
p_hex = font_version_hex;
strToHex(p_ch,p_hex);
int k = hexChartoByte(font_version_hex,font_version_byte);
//填充版本号数据
for(int i = 0;i<n;i++)
printf ("%X ",0XFF & mcu_version_byte[i]);
for(int i = 0;i<m;i++)
printf ("%X ",0XFF & ble_version_byte[i]);
for(int i = 0;i<k;i++)
printf ("%X ",0XFF & font_version_byte[i]);
hexToStr(p_hex, p_result);
printf("the string is:%s\n", p_result);
}
以上demo将字符串转换成utf8的字节流，可用utf8的转换工具（LoveString）还原成字符串验证。
5、union与数据的拆分与合并以及大小端的判断
1) 将int型的i拆分成4字节char型的c
#include<stdio.h>
union var{
char c[4];
int i;
};
int main(){
union var data;
data.i = 0x11020304;
printf("%x\n",data.c[0]);
printf("%x\n",data.c[1]);
printf("%x\n",data.c[2]);
printf("%x\n",data.c[3]);
return 0;
}
2) 合并就是反过来
#include<stdio.h>
union var{
char c[4];
int i;
};
int main(){
union var data;
data.c[0] = 0x04;
data.c[1] = 0x03;
data.c[2] = 0x02;
data.c[3] = 0x11;
printf("%x\n",data.i);
return 0; }
3) 大小端的判断
#include<stdio.h>
union var{
char c[4];
int i;
};
int main(){
union var data;
data.i = 0x11020304;
printf("%x\n",data.c[0]);
printf("%x\n",data.c[1]);
printf("%x\n",data.c[2]);
printf("%x\n",data.c[3]);
if( data.c[0] == 0x11 )
{
printf("Systerm is BigEndian");
}
return 0;
}
4、连接符#的应用
1) 连接数值类型用双#
#include <stdio.h>
#define COMB(a,b,c) a##b##c
void main()
{
printf("%d\n",COMB(1,2,3));
}
2) 连接字符类型用单#
#include <stdio.h>
#define CATSTR(n) "abcd"#n
void main()
{
printf("%s\n",CATSTR(100));
}
3、 时间转换(localtime和mktime)
有些系统没有localtime和mketime, 把linux内核里边这两函数扣出来用。
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <stdint.h>
struct tm {
/*
* the number of seconds after the minute, normally in the range
* 0 to 59, but can be up to 60 to allow for leap seconds
*/
int tm_sec;
/* the number of minutes after the hour, in the range 0 to 59*/
int tm_min;
/* the number of hours past midnight, in the range 0 to 23 */
int tm_hour;
/* the day of the month, in the range 1 to 31 */
int tm_mday;
/* the number of months since January, in the range 0 to 11 */
int tm_mon;
/* the number of years since 1900 */
long tm_year;
/* the number of days since Sunday, in the range 0 to 6 */
int tm_wday;
/* the number of days since January 1, in the range 0 to 365 */
int tm_yday;
int tm_isdst;
};
static unsigned long mktime(const unsigned int year0, const unsigned int mon0,
const unsigned int day, const unsigned int hour,
const unsigned int min, const unsigned int sec)
{
unsigned int mon = mon0, year = year0;
/* 1..12 -> 11,12,1..10 */
if (0 >= (int) (mon -= 2)) {
mon += 12; /* Puts Feb last since it has leap day */
year -= 1;
}
return ((((unsigned long)
(year/4 - year/100 + year/400 + 367*mon/12 + day) +
year*365 - 719499
)*24 + hour /* now have hours */
)*60 + min /* now have minutes */
)*60 + sec; /* finally seconds */
}
static struct tm * localtime_r(time_t *srctime,struct tm *tm_time)
{
long int n32_Pass4year,n32_hpery;
const static char Days[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const static int ONE_YEAR_HOURS = 8760;
time_t time = *srctime;
time=time+28800;
tm_time->tm_isdst=0;
if(time < 0)
{
time = 0;
}
tm_time->tm_sec=(int)(time % 60);
time /= 60;
tm_time->tm_min=(int)(time % 60);
time /= 60;
tm_time->tm_wday=(time/24+4)%7;
n32_Pass4year=((unsigned int)time / (1461L * 24L));
tm_time->tm_year=(n32_Pass4year << 2)+70;
time %= 1461L * 24L;
tm_time->tm_yday=(time/24)%365;
for (;;)
{
n32_hpery = ONE_YEAR_HOURS;
if ((tm_time->tm_year & 3) == 0)
{
n32_hpery += 24;
}
if (time < n32_hpery)
{
break;
}
tm_time->tm_year++;
time -= n32_hpery;
}
tm_time->tm_hour=(int)(time % 24);
time /= 24;
time++;
if ((tm_time->tm_year & 3) == 0)
{
if (time > 60)
{
time--;
}
else
{
if (time == 60)
{
tm_time->tm_mon = 1;
tm_time->tm_mday = 29;
return tm_time;
}
}
}
for (tm_time->tm_mon = 0;Days[tm_time->tm_mon] < time;tm_time->tm_mon++)
{
time -= Days[tm_time->tm_mon];
}
tm_time->tm_mday = (int)(time);
return tm_time;
}
int main(void)
{
uint32_t now = 1451577600; /*2016/01/01 00:00:00*/
struct tm tm = {0};
char *wday[] = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
localtime_r(&now, &tm);
printf("%d/%d/%d \n", 1900 + tm.tm_year, 1 + tm.tm_mon, tm.tm_mday);
printf("%s %d:%d:%d \n", wday[tm.tm_wday], tm.tm_hour, tm.tm_min, tm.tm_sec);
now = mktime(1900 + tm.tm_year, 1 + tm.tm_mon, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec);
printf("rtc value : %d\n", now);
return 0;
}
2、函数指针（数组）的应用以及参数传递
//预存的APP响应
void (*CmdCallbackArray[APP_CMD_MAX])(uint8_t *para) = {
0 ,
FirewareManageCallback , // FirewareManage = 1
DataSyncCallback ,
SetCmdCallback,
HintCmdCallback,
0,
BindCallback,
FactoryTestCallback,
LogCtrlCallback
};
bool App_Data_L1_DataParse( uint8_t *L1_Packet,uint8_t *L1_Payload){
bool ret=true;
uint8_t para[60] = {0};
uint16_t L2_len = 0;
uint16_t check_sum = 0;
L2_len =((((uint16_t)L1_Packet[5])<<8)|((uint16_t)L1_Packet[6]));
check_sum = CRC_calc(&L1_Packet[9] , &L1_Packet[9+L2_len]);
if( ( (((uint16_t)L1_Packet[7])<<8)|((uint16_t)L1_Packet[8]) ) == check_sum )
{
//正常接收，进入L2_Command_Content
para[0] = L1_Packet[2];
memcpy(¶[1],&L1_Packet[10],L2_len-1);
CmdCallbackArray[L1_Packet[9]](para);
}
return ret;
}
工作多年，C语言基础还是不扎实，惭愧！
eg.
a.简单实例
#include<stdlib.h>
#include<stdio.h>
#include<stdint.h>
int main()
{
uint8_t test[8]={1};
struct b_t {
uint8_t *data;
};
struct a_t {
struct b_t *b;
};
struct a_t *a = (struct a_t*)malloc(sizeof(struct a_t));
a->b = (struct b_t*)malloc(sizeof(struct b_t));
a->b->data = malloc(8*sizeof(uint8_t));
a->b->data = test;
printf("%d\r\n",*(a->b->data));
return 0;
}
b.一个具体的的应用，某beacon的蓝牙广播封包
#include<stdlib.h>
#include<stdio.h>
#include<stdint.h>
struct event_t {
uint16_t id;
uint8_t data_len;
uint8_t *data;
};
struct manufacturer_data_t{
uint8_t data_len;
uint8_t *data;
};
struct manufacturer_title_data_t{
uint8_t data_len;
uint8_t *data;
};
struct x_beacon_t {
uint8_t length;
uint8_t bt_sig_type;
uint16_t x_service_uuid;
uint16_t frame_control;
uint16_t product_id;
uint32_t frame_counter;
uint8_t mac_add;
uint8_t capability;
struct event_t *event;
struct manufacturer_data_t *manufacturer_data;
struct manufacturer_title_data_t *manufacturer_title_data;
}*x_beacon;
int main(void)
{
uint8_t test[8]={1};
x_beacon = (struct x_beacon_t *)malloc(sizeof(struct x_beacon_t));
x_beacon->event = (struct event_t*)malloc(sizeof(struct event_t));
x_beacon->event->data = (uint8_t*)malloc(8*sizeof(uint8_t));
x_beacon->event->data = test;
x_beacon->manufacturer_data = (struct manufacturer_data_t*)malloc(sizeof(struct manufacturer_data_t));
x_beacon->manufacturer_title_data = (struct manufacturer_title_data_t*)malloc(sizeof(struct manufacturer_title_data_t));
x_beacon->length = 0x09;
x_beacon->bt_sig_type = 0x16;
x_beacon->x_service_uuid = 0xfe95;
x_beacon->frame_control = 0x1021;
x_beacon->product_id = 0x0157;
x_beacon->frame_counter = 0x00;
x_beacon->capability = 0x09;
printf("%0x\r\n",x_beacon->x_service_uuid);
printf("%0d\r\n",*(x_beacon->event->data));
return 0;
}