标签：emc [] 源代码 字符串 const include eof cte 溢出
#include <stdio.h>
#include <assert.h>
/*
* 作用：获取串str的长度
*/
int strlen(const char *pcStr)
{
assert(pcStr != NULL);
int iLen = 0;
while (‘\0‘ != *pcStr)
{
pcStr++;
iLen++;
}
return iLen;
}
/*
* 前提：strDes指向的内存至少能够容纳(strlen(strDes) + strlen(strSrc) + 1) bytes
* 作用：将串strSrc连接到串strDes的末尾，函数本身不保证安全（使用不当会内存溢出）
*/
char *strcat(char *pcStrDest, const char *pcStrSrc)
{
assert((pcStrDest != NULL) && (pcStrSrc != NULL));
char *pcTemp = pcStrDest;
/* pcStrDes指针指向串pcStrDes的末尾 */
while (‘\0‘ != *pcStrDest)
{
pcStrDest++;
}
/* 依次从源串pcStrSrc不断拷贝字符到目的串pcStrDes中 */
while (‘\0‘ != *pcStrSrc)
{
*pcStrDest = *pcStrSrc;
pcStrSrc++;
pcStrDest++;
}
*pcStrDest = *pcStrSrc;
return pcTemp;
}
/*
* 前提：strDes指向的内存至少能够容纳(strlen(strSrc) + 1) bytes
* 作用：将串strSrc拷贝到strDes指向的内存空间，函数本身不保证安全（使用不当会内存溢出）
*/
char *strcpy(char *pcStrDest, const char *pcStrSrc)
{
assert((pcStrDest != NULL) && (pcStrSrc != NULL));
char *pcTemp = pcStrDest;
while (‘\0‘ != *pcStrSrc)
{
*pcStrDest = *pcStrSrc;
pcStrSrc++;
pcStrDest++;
}
*pcStrDest = *pcStrSrc;
return pcTemp;
}
/*
* 作用：按字典序比较串s和串t的大小
*/
int strcmp(const char *pcStrA, const char *pcStrB)
{
assert((pcStrA != NULL) && (pcStrB != NULL));
while ((‘\0‘ != *pcStrA) && (‘\0‘ != *pcStrB) && (*pcStrA == *pcStrB))
{
pcStrA++;
pcStrB++;
}
return (int)(*pcStrA - *pcStrB);
}
/*
* 前提：strDes指向的内存至少能够容纳(strlen(strDes) + count + 1) bytes
* 作用：将串strSrc的前count个字符连接到串strDes的末尾，函数本身不保证安全（使用不当会内存溢出）
*/
char *strncat(char *pcStrDest, const char *pcStrSrc, int iCount)
{
assert((pcStrDest != NULL) && (pcStrSrc != NULL));
char *pcTemp = pcStrDest;
while (‘\0‘ != *pcStrDest)
{
pcStrDest++;
}
while ((iCount > 0) && (‘\0‘ != *pcStrSrc))
{
*pcStrDest = *pcStrSrc;
pcStrSrc++;
pcStrDest++;
iCount--;
}
*pcStrDest = ‘\0‘;
return pcTemp;
}
/*
* 前提：strDes指向的内存至少能够容纳(count + 1) bytes
* 作用：将串strSrc的前count个字符拷贝到strDes指向的内存空间，函数本身不保证安全（使用不当会内存溢出）
*/
char *strncpy(char *pcStrDest, const char *pcStrSrc, int iCount)
{
assert((pcStrDest != NULL) && (pcStrSrc != NULL));
char *pcTemp = pcStrDest;
while ((iCount > 0) && (‘\0‘ != pcStrSrc))
{
*pcStrDest = *pcStrSrc;
pcStrSrc++;
pcStrDest++;
iCount--;
}
return pcTemp;
}
/*
* 作用：按字典序比较串s和串t的前count个字符的大小
*/
int strncmp(const char *pcStrA, const char *pcStrB, int iCount)
{
assert((pcStrA != NULL) && (pcStrB != NULL));
while ((‘\0‘ != *pcStrA) && (‘\0‘ != *pcStrB) && (*pcStrA == *pcStrB) &&
(iCount > 0))
{
iCount--;
if (0 == iCount)
{
break;
}
pcStrA++;
pcStrB++;
}
return (int)(*pcStrA - *pcStrB);
}
/*
* 前提：dest指向的内存能够容纳count bytes
* 作用：将src所指向内存的count bytes拷贝到的dest指向的内存
*/
void *memcpy(void *pvDest, const void *pvSrc, int iCount)
{
assert((pvDest != NULL) && (pvSrc != NULL));
void *pvTemp = pvDest;
char *pcDest = (char *)pvDest;
const char *pcSrc = (const char *)pvSrc;
while (iCount > 0)
{
*pcDest = *pcSrc;
pcDest++;
pcSrc++;
iCount--;
}
return pvTemp;
}
/*
* 作用：将str的前count个字节置为字符c
*/
void *memset(void *pvSrc, int iCh, int iCount)
{
assert(pvSrc != NULL);
char *pcSrc = (char *)pvSrc;
while (iCount > 0)
{
*pcSrc = (char)iCh;
pcSrc++;
iCount--;
}
return pvSrc;
}
/*
* 作用：将src所指向内存的count bytes拷贝到的dest指向的内存(解决了memcpy未解决的内存重叠问题)
*/
void *memmove(void *pvDest, const void *pvSrc, int iCount)
{
assert((pvDest != NULL) && (pvSrc != NULL));
void *pvTemp = pvDest;
char *pcDest = (char *)pvDest;
const char *pcSrc = (const char *)pvSrc;
// 逻辑：
// 1）在src小于dest前提下，然后判断src+count指向的内存是否与dest指向的内存重叠
// 2) 如果重叠则从src+count开始复制，复制到dest+count，从后往前拷贝count字节
if ((pvSrc < pvDest) && (pvSrc + iCount > pvDest))
{
pcDest = pcDest + iCount - 1;
pcSrc = pcSrc + iCount - 1;
while (iCount > 0)
{
*pcDest = *pcSrc;
pcDest--;
pcSrc--;
iCount--;
}
}
else
{
while (iCount > 0)
{
*pcDest = *pcSrc;
*pcDest++;
*pcSrc++;
iCount--;
}
}
return pvTemp;
}
int main()
{
int iLen = 0;
int iRet = 0;
char acBuffer[4] = {0};
char *pcTestStr1 = "Today is sunday.";
char acTestStr2[] = "Today";
char acTestStr3[] = "Today is sunday.";
char acTestStr4[sizeof("Today is ") + sizeof("sunday.") - 1] = "Today is ";
iLen = strlen(pcTestStr1);
printf("iLen = %d\n", iLen);
(void)strncpy(acBuffer, pcTestStr1, sizeof(acBuffer) - 1);
printf("acBuffer:%s\n", acBuffer);
iRet = strncmp(pcTestStr1, acTestStr2, strlen(acTestStr2));
printf("strncmp iRet = %d\n", iRet);
iRet = strcmp(pcTestStr1, acTestStr2);
printf("strcmp iRet = %d\n", iRet);
(void)memmove(&acTestStr3[1], &acTestStr3[0], strlen("Today"));
printf("memmove acTestStr3:%s\n", acTestStr3);
printf("before strncat acTestStr4:%s\n", acTestStr4);
(void)strncat(acTestStr4, "sunday.111",
sizeof(acTestStr4) - strlen(acTestStr4) - 1);
printf("after strncat acTestStr4:%s\n", acTestStr4);
return 0;
}标签：emc [] 源代码 字符串 const include eof cte 溢出
原文地址：http://blog.51cto.com/bocaihaoci/2331100
