[導(dǎo)讀]導(dǎo)讀：怎么做好嵌入式？相信這個問題無論問誰你都會得到一句 學好C語言！ 今天推薦一篇大佬寫的嵌入式C語言知識點總結(jié)，非常值得一讀。 從語法上來說C語言并不復(fù)雜， 但編寫優(yōu)質(zhì)可靠的嵌入式C程序并非易事，不僅需要熟知硬件特性和缺陷，還需要對編譯原理和計
關(guān)鍵字
數(shù)據(jù)類型
typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned int uint32_t;
......
typedef signed int int32_t;
printf("int size:%d, short size:%d, char size:%d\n", sizeof(int), sizeof(char), sizeof(short));
char *p；
printf("point p size:%d\n", sizeof(p));
內(nèi)存管理和存儲架構(gòu)
//main.c#include <stdio.h>#include <stdlib.h>
static int st_val; //靜態(tài)全局變量 -- 靜態(tài)存儲區(qū)
int ex_val; //全局變量 -- 靜態(tài)存儲區(qū)int main(void)
{
int a = 0; //局部變量 -- 棧上申請
int *ptr = NULL; //指針變量
static int local_st_val = 0; //靜態(tài)變量
local_st_val += 1;
a = local_st_val;
ptr = (int *)malloc(sizeof(int)); //從堆上申請空間
if(ptr != NULL)
{
printf("*p value:%d", *ptr);
free(ptr);
ptr = NULL;
//free后需要將ptr置空，否則會導(dǎo)致后續(xù)ptr的校驗失效，出現(xiàn)野指針
}
}
LD_ROM 0x00800000 0x10000 { ;load region size_region
EX_ROM 0x00800000 0x10000 { ;load address = execution address
(RESET, +First)
*(InRoot$$Sections)
(+RO)
}
EX_RAM 0x20000000 0xC000 { ;rw Data
(+RW +ZI)
}
EX_RAM1 0x2000C000 0x2000 {
.ANY(MySection)
}
EX_RAM2 0x40000000 0x20000{
.ANY(Sdram)
}
}
int a[10] __attribute__((section("Mysection")));
int b[100] __attribute__((section("Sdram")));
指針和數(shù)組
int main(void)
{
char cval[] = "hello";
int i;
int ival[] = {1, 2, 3, 4};
int arr_val[][2] = {{1, 2}, {3, 4}};
const char *pconst = "hello";
char *p;
int *pi;
int *pa;
int **par;
p = cval;
p++; //addr增加1
pi = ival;
pi+=1; //addr增加4
pa = arr_val[0];
pa+=1; //addr增加4
par = arr_val;
par++; //addr增加8
for(i=0; i<sizeof(cval); i++)
{
printf("%d ", cval[i]);
}
printf("\n");
printf("pconst:%s\n", pconst);
printf("addr:%d, %d\n", cval, p);
printf("addr:%d, %d\n", icval, pi);
printf("addr:%d, %d\n", arr_val, pa);
printf("addr:%d, %d\n", arr_val, par);
}
/* PC端64位系統(tǒng)下運行結(jié)果
0x68 0x65 0x6c 0x6c 0x6f 0x0
pconst:hello
addr:6421994, 6421995
addr:6421968, 6421972
addr:6421936, 6421940
addr:6421936, 6421944 */
typedef struct
{
int b;
int a;
}STRUCT_VAL;
static __align(4) char arr[8] = {0x12, 0x23, 0x34, 0x45, 0x56, 0x12, 0x24, 0x53};
int main(void)
{
STRUCT_VAL *pval;
int *ptr;
pval = (STRUCT_VAL *)arr;
ptr = (int *)&arr[4];
printf("val:%d, %d", pval->a, pval->b);
printf("val:%d,", *ptr);
}
//0x45342312 0x53241256
//0x53241256
typedef int (*pfunc)(int, int);
int func_add(int a, int b){
return a+b;
}
int main(void)
{
pfunc *func_ptr;
*（volatile uint32_t *）0x20001000 = 0x01a23131;
func_ptr = func_add;
printf("%d\n", func_ptr(1, 2));
}
結(jié)構(gòu)類型和對齊
typedef enum {spring=1, summer, autumn, winter }season;
season s1 = summer;
typedef union{
char c;
short s;
int i;
}UNION_VAL;
UNION_VAL val;
int main(void)
{
printf("addr:0x%x, 0x%x, 0x%x\n",
(int)(&(val.c)), (int)(&(val.s)), (int)(&(val.i)));
val.i = 0x12345678;
if(val.s == 0x5678)
printf("小端模式\n");
else
printf("大端模式\n");
}
/*
addr:0x407970, 0x407970, 0x407970
小端模式
*/
int data = 0x12345678;
short *pdata = (short *)&data;
if(*pdata = 0x5678)
printf("%s\n", "小端模式");
else
printf("%s\n", "大端模式");
typedef int (*pfunc)(int, int);
typedef struct{
int num;
int profit;
pfunc get_total;
}STRUCT_VAL;
int GetTotalProfit(int a, int b)
{
return a*b;
}
int main(void){
STRUCT_VAL Val;
STRUCT_VAL *pVal;
Val.get_total = GetTotalProfit;
Val.num = 1;
Val.profit = 10;
printf("Total:%d\n", Val.get_total(Val.num, Val.profit)); //變量訪問
pVal = &Val;
printf("Total:%d\n", pVal->get_total(pVal->num, pVal->profit)); //指針訪問
}
/*
Total:10
Total:10
*/
typedef unsigned char uint8_t;
union reg{
struct{
uint8_t bit0:1;
uint8_t bit1:1;
uint8_t bit2_6:5;
uint8_t bit7:1;
}bit;
uint8_t all;
};
int main(void)
{
union reg RegData;
RegData.all = 0;
RegData.bit.bit0 = 1;
RegData.bit.bit7 = 1;
printf("0x%x\n", RegData.all);
RegData.bit.bit2_6 = 0x3;
printf("0x%x\n", RegData.all);
}
/*
0x81
0x8d
*/
union DATA{
int a;
char b;
};
struct BUFFER0{
union DATA data;
char a;
//reserved[3]
int b;
short s;
//reserved[2]
}; //16字節(jié)
struct BUFFER1{
char a;
//reserved[0]
short s;
union DATA data;
int b;
};//12字節(jié)
int main(void)
{
struct BUFFER0 buf0;
struct BUFFER1 buf1;
printf("size:%d, %d\n", sizeof(buf0), sizeof(buf1));
printf("addr:0x%x, 0x%x, 0x%x, 0x%x\n",
(int)&(buf0.data), (int)&(buf0.a), (int)&(buf0.b), (int)&(buf0.s));
printf("addr:0x%x, 0x%x, 0x%x, 0x%x\n",
(int)&(buf1.a), (int)&(buf1.s), (int)&(buf1.data), (int)&(buf1.b));
}
/*
size:16, 12
addr:0x61fe10, 0x61fe14, 0x61fe18, 0x61fe1c
addr:0x61fe04, 0x61fe06, 0x61fe08, 0x61fe0c
*/
預(yù)處理機制
printf("error loop\n");\
}while(0);
int global(v) = 10;
int global(add)(int a, int b)
{
return a+b;
｝
struct TestA
{
char i;
int b;
}A;
等同于
struct _TestB{
char i;
int b;
}__attribute__((packed))A;
總結(jié)
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