如何正確使用動態內存?
原文:https://blog.csdn.net/jiangjunjie_2005/article
一. 常見錯誤與預防
1. 分配後忘記釋放內存
void func(void)
{
p = malloc(len);
do_something(p);
return; /*錯誤!退出程序時沒有釋放內存*/
}
預防: 編寫代碼時 malloc() 和 free() 保證成對出現,避免忘記資源回收。
int func(void)
{
p = malloc(len);
if (condition)
return -1; /*錯誤!退出程序時沒有釋放內存*/
free(p);
return 0;
}
預防: 一旦使用動態內存分配,請仔細檢查程序的退出分支是否已經釋放該動態內存。
2. 釋放內存調用錯誤指針
void func(void)
{
p = malloc(len);
val = *p++; /*錯誤!動態內存句柄不可移動*/
free(p);
}
預防: 千萬不要修改動態內存句柄!可以另外賦值給其他指針變量,再對該動態內存進行訪問操作。
3. 分配內存不夠導致溢出
void func(void)
{
len = strlen(str);
p = malloc(len);
strcpy(p, str); /*錯誤!str的’\0’寫到動態內存外*/
}
預防: 分配內存前仔細思考長度是否足夠,千萬注意字符串拷貝佔用內存比字符串長度大 1。
二. 自動查錯機制
儘管在開發過程中堅守原則和謹慎編程甚至嚴格測試,然而內存泄露的錯誤還是難以杜絕,如何讓系統自動查出內存泄露的錯誤呢?
一種比較好的方法是建立日誌塊,即每次分配內存時記錄該內存塊的指針和大小,釋放時再去除該日誌塊,如果有內存泄露就會有對應的日誌塊記錄這些內存沒有釋放,這樣就可以提醒程序員進行查錯。
有了上述日誌塊操作函數,再來實現動態內存分配與釋放函數就很容易了。只有當處於 DEBUG 版本和打開內存調試 DMEM_DBG 時才進行日誌登錄,否則 MallocExt() 和 FreeExt() 函數與 malloc() 和 free() 是等價的,這樣保證了系統處於發佈版本時的性能。
(代碼已經過嚴格測試,但這不是盈利的商業代碼,即沒有版權。但如果因代碼錯誤帶來的任何損失作者具有免責權利)
代碼部分:
首先定義日誌塊結構體:
/* Log of dynamic memory usage */
typedef struct _dmem_log
{
struct _dmem_log *p_stNext; /* Point to next log */
const void *p_vDMem; /* Point to allocated memory by this pointer */
INT32S iSize; /* Size of the allocated memory */
} DMEM_LOG;
然後爲該結構體開闢內存:
static DMEM_LOG *s_pstFreeLog; /* Point to free log pool by this pointer */
static INT8U s_byNumUsedLog;
static DMEM_LOG *s_pstHeadLog; /* Point to used log chain by this pointer */
/* Pool of dynamic memory log */
#define NUM_DMEM_LOG 20
static DMEM_LOG s_astDMemLog[NUM_DMEM_LOG];
下面是內存日誌塊的操作函數:初始化、插入日誌和移除日誌:
/********************************************************** * Initialize DMem Log
* Description : Initialize log of dynamic memory
* Arguments : void
* Returns : void
* Notes :
**********************************************************/
static void InitDMemLog(void)
{
INT16S nCnt;
/* Initialize pool of log */
for (nCnt = 0; nCnt < NUM_DMEM_LOG; ++nCnt)
{
/* Point to next one */
s_astDMemLog[nCnt].p_stNext = &s_astDMemLog[nCnt + 1];
}
s_astDMemLog[NUM_DMEM_LOG - 1].p_stNext = NULL;
s_pstFreeLog = &s_astDMemLog[0]; /* Point to the 1th log */
return;
}
/********************************************************** * Log DMem
* Description : Join an allocated memory into log pool
* Arguments : const void *p_vAddr point to address of this allocated memory by this pointer
* INT32S iSize size of this allocated memory
* Returns : void
* Notes :
**********************************************************/
static void LogDMem(const void *p_vAddr, INT32S iSize)
{
ASSERT(p_vAddr && iSize > 0);
DMEM_LOG *p_stLog;
#if OS_CRITICAL_METHOD == 3
OS_CPU_SR cpu_sr;
#endif
/* Get a log from free pool */
OS_ENTER_CRITICAL(); /* Avoid race condition on s_pstFreeLog */
if (!s_pstFreeLog)
{
OS_EXIT_CRITICAL();
PRINTF("Allocate DMemLog failed.\r\n");
return;
}
p_stLog = s_pstFreeLog;
s_pstFreeLog = s_pstFreeLog->p_stNext;
OS_EXIT_CRITICAL();
/* Don't need to protect this log that is free one currently */
p_stLog->p_vDMem = p_vAddr;
p_stLog->iSize = iSize;
/* Put this log into used chain */
OS_ENTER_CRITICAL(); /* Avoid race condition */
p_stLog->p_stNext = s_pstHeadLog;
s_pstHeadLog = p_stLog;
++s_byNumUsedLog;
OS_EXIT_CRITICAL();
return;
}
/********************************************************** * Unlog DMem
* Description : Remove an allocated memory from log pool
* Arguments : const void *p_vAddr point to address of this allocated memory by this pointer
* Returns : void
* Notes :
**********************************************************/
static void UnlogDMem(const void *p_vAddr)
{
ASSERT(p_vAddr);
DMEM_LOG *p_stLog, *p_stPrev;
#if OS_CRITICAL_METHOD == 3
OS_CPU_SR cpu_sr;
#endif
/* Search the log */
OS_ENTER_CRITICAL(); /*Avoid race condition */
p_stLog = p_stPrev = s_pstHeadLog;
while (p_stLog)
{
if (p_vAddr == p_stLog->p_vDMem)
{
break; /* Have found */
}
p_stPrev = p_stLog;
p_stLog = p_stLog->p_stNext; /* Move to next one */
}
if (!p_stLog)
{
OS_EXIT_CRITICAL();
PRINTF("Search Log failed.\r\n");
return;
}
/* Remove from used pool */
if (p_stLog == s_pstHeadLog)
{
s_pstHeadLog = s_pstHeadLog->p_stNext;
}
else
{
p_stPrev->p_stNext = p_stLog->p_stNext;
}
--s_byNumUsedLog;
OS_EXIT_CRITICAL();
/* Don't need to protect this log that is free one currently */
p_stLog->p_vDMem = NULL;
p_stLog->iSize = 0;
/* Add into free pool */
OS_ENTER_CRITICAL(); /* Avoid race condition */
p_stLog->p_stNext = s_pstFreeLog;
s_pstFreeLog = p_stLog;
OS_EXIT_CRITICAL();
return;
}
帶日誌記錄功能的內存分配 MallocExt() 和內存釋放 FreeExt() 函數:
/*********************************************************
* Malloc Extension
* Description : Malloc a block of memory and log it if need
* Arguments : INT32S iSize size of desired allocate memory
* Returns: void *NULL= failed, otherwise=pointer of allocated memory
* Notes :
**********************************************************/
void *MallocExt(INT32S iSize)
{
ASSERT(iSize > 0);
void *p_vAddr;
p_vAddr = malloc(iSize);
if (!p_vAddr)
{
PRINTF("malloc failed at %s line %d.\r\n", __FILE__, __LINE__);
}
else
{
#if (DMEM_DBG && DBG_VER)
memset(p_vAddr, 0xA3, iSize); /* Fill gargage for debug */
LogDMem(p_vAddr, iSize); /* Log memory for debug */
#endif
}
return p_vAddr;
}
/**********************************************************
* Free Extension
* Description : Free a block of memory and unlog it if need
* Arguments : void * p_vMem point to the memory by this pointer
* Returns : void
* Notes :
**********************************************************/
void FreeExt(void *p_vMem)
{
ASSERT(p_vMem);
free(p_vMem);
#if (DMEM_DBG && DBG_VER)
UnlogDMem(p_vMem); /* Remove memory from log */
#endif
return;
}
本文由 Readfog 進行 AMP 轉碼,版權歸原作者所有。
來源:https://mp.weixin.qq.com/s/rNy70kODxD1srGZvr5z7GQ