标签：style blog color 使用 os io 数据 for
1.变量:一段存储区域,每个变量都有一个地址,指向变量的存储位置.
变量名:变量名对应变量的地址.(编译器会将程序中的变量地址和变量名,建立一个"符号表",编写代码时对变量的操作,实际编译器会拿 符号表中变量名对应的
地址中存储的数据进行操作.)
2.指针是个变量,变量里面存储的值用来当作地址.
char *p;
p是变量,存储的值是一个地址.(p本身也有地址,&p)
3.二维指针:
char **p;
p存储的是一个指针的地址.(p本身也有地址,&p)
4.指针和数组
char a[10];
char *p;
区别: a == &a;
p != &p;
5.u/cos ii 的指针的运用.
OS_MEM *OSMemCreate (void *addr, INT32U nblks, INT32U blksize, INT8U *perr) { OS_MEM *pmem; INT8U *pblk; void **plink; INT32U loops; INT32U i; // ... OS_ENTER_CRITICAL(); pmem = OSMemFreeList; /* Get next free memory partition */ if (OSMemFreeList != (OS_MEM *)0) { /* See if pool of free partitions was empty */ OSMemFreeList = (OS_MEM *)OSMemFreeList->OSMemFreeList; } OS_EXIT_CRITICAL(); if (pmem == (OS_MEM *)0) { /* See if we have a memory partition */ *perr = OS_ERR_MEM_INVALID_PART; return ((OS_MEM *)0); } plink = (void **)addr; /* Create linked list of free memory blocks */ pblk = (INT8U *)addr; loops = nblks - 1u; for (i = 0u; i < loops; i++) { pblk += blksize; /* Point to the FOLLOWING block */ *plink = (void *)pblk; /* Save pointer to NEXT block in CURRENT block */ plink = (void **)pblk; /* Position to NEXT block */ } *plink = (void *)0; /* Last memory block points to NULL */ pmem->OSMemAddr = addr; /* Store start address of memory partition */ pmem->OSMemFreeList = addr; /* Initialize pointer to pool of free blocks */ pmem->OSMemNFree = nblks; /* Store number of free blocks in MCB */ pmem->OSMemNBlks = nblks; pmem->OSMemBlkSize = blksize; /* Store block size of each memory blocks */ *perr = OS_ERR_NONE; return (pmem); }
摘取一段:
plink = (void **)addr; /* Create linked list of free memory blocks */ pblk = (INT8U *)addr; loops = nblks - 1u; for (i = 0u; i < loops; i++) { pblk += blksize; /* Point to the FOLLOWING block */ *plink = (void *)pblk; /* Save pointer to NEXT block in CURRENT block */ plink = (void **)pblk; /* Position to NEXT block */ } *plink = (void *)0; /* Last memory block points to NULL */
其中
plink = (void **)addr; pblk = (INT8U *)addr;
乍一看,很高深的样子,addr本身是一维的,怎么既作为一维指针,又作为二维指针使用.
但看看后面plink的使用,plink只是取一维的深度来用,也就是说等价以下代码:
void *plink; plink = (void *)addr; /* Create linked list of free memory blocks */ pblk = (INT8U *)addr; loops = nblks - 1u; for (i = 0u; i < loops; i++) { pblk += blksize; /* Point to the FOLLOWING block */ *plink = (void *)pblk; /* Save pointer to NEXT block in CURRENT block */ plink = (void *)pblk; /* Position to NEXT block */ } *plink = (void *)0; /* Last memory block points to NULL */
标签：style blog color 使用 os io 数据 for
原文地址：http://www.cnblogs.com/waefk/p/3878788.html
