strcpy strlen memcpy strcat strcmp strstr strrev函数的实现代码

/* //strcpy函数的实现，注意命名要与原来的库函数有区别 #include <iostream>#include <cstdio>#include <assert.h>using namespace std;char *mystrcpy(char *strDest, const char *strSrc){     if ((strDest == NULL) || (strSrc == NULL))//保证strDest和strSrc的有效性          return NULL;     char *strDestCopy = strDest;//保存目标字符串的首地址，以便最后的返回      //注意：++的优先级要比*的要高      while ((*strDest++ = *strSrc++) != '\0');//将字符从strsrc中复制到strDest中      return strDestCopy; }int main(){    char *strSrc = "Hello World!";    char strDest[20];    mystrcpy(strDest, strSrc);    printf("strDest:%s\n", strDest);         system("pause");}*//* //strlen函数的实现，有两种方法实现#include <iostream>#include <cstdio>#include <assert.h>using namespace std;//第一种方法就是通过一个变量len的自增，直至遇到字符串的结束字符 int mystrlen1(const char *strSrc){    assert(strSrc != NULL);//保证字符串首地址的有效性     int len = 0;//结果的保存     while (*strSrc++ != '\0'){          len++;     }     return len; } //第二种方法就是通过对字符串首地址的保存，再用字符串的末地址减去首地址就可以int mystrlen2(char *strSrc){    int len;     char *tmpstrSrc = strSrc;//将字符串的首地址先保存下来     while (*strSrc++ != '\0'); //直至遇到字符串的结束符，strSrc已经为字符串的末地址     len = (strSrc - tmpstrSrc - 1);//末地址减去首地址，得出结果     return len; } int main(){    char *strSrc = "Hello World!";    int len1, len2;    len1 = mystrlen1(strSrc);    len2 = mystrlen2(strSrc);     printf("len1 = %d\n", len1);    printf("len2 = %d\n", len2);         system("pause"); } *//* //memcpy函数的实现 #include <iostream>#include <cstdio>#include <assert.h>using namespace std;void *mymemcpy(void *memTo, const void *memFrom, int size){    assert((memTo != NULL) && (memFrom != NULL));//保证字符串的有效性    char *tmpmemTo = (char *)memTo;//对字符串首地址的保存     char *tmpmemFrom = (char *)memFrom;     //按照size的大小进行复制     while (size-- > 0){          *tmpmemTo++ = *tmpmemFrom++;     }     return memTo; } int main(){    char *strFrom = "Hello World!";    char strTo[20];    mymemcpy(strTo, strFrom, 6);    strTo[6] = '\0';    printf("strTo:%s\n", strTo);         system("pause"); } *//* //strcat函数的实现#include <iostream>#include <cstdio>#include <assert.h>using namespace std;char *mystrcat(char *strDest, char *strSrc){     char *tmpstrDest;     tmpstrDest = strDest;//保存目标字符串的首地址      while (*strDest++ != '\0');// 循环到字符串的末尾      strDest--;      while ((*strDest++ = *strSrc++) != '\0');//进行字符串的复制      return tmpstrDest; //字符串首地址的返回 } int main(){    char *strDest = NULL;     char *strSrc1 = "Hello ";    char *strSrc2 = "World!";    strDest = (char *)malloc(256);    *strDest = '\0';    mystrcat(mystrcat(strDest, strSrc1), strSrc2);    printf("strDest:%s\n", strDest);    free(strDest);    strDest = NULL;         system("pause"); } *//* //strcmp函数的实现#include <iostream>#include <cstdio>using namespace std;int mystrcmp(const char *strSrc, const char *strDest){    int ans = 0;//结果的保存     //取两个字符串的各个字符进行相减，即是它们的ASCII相减     while (!(ans = *(unsigned char *)strSrc - *(unsigned char *)strDest) && *strDest){          ++strSrc;          ++strDest;     }     if (ans > 0)        ans = 1;    else if (ans < 0)        ans = -1;    return ans; } int main(){    char *str = "1234567";    char *str1 = "1234567";    char *str2 = "12345678";    char *str3 = "1234566";        int test1 = mystrcmp(str, str1);    int test2 = mystrcmp(str, str2);    int test3 = mystrcmp(str, str3);        cout << test1 << endl << test2 << endl << test3 << endl;         system("pause"); } *//* //strstr函数的实现#include <iostream>#include <cstdio>using namespace std;int mystrstr(const char *strSrc, const char *strSub){    int pos = 0;    //对两个字符串的首地址进行保存     const char *bp;     const char *sp;    if (strSrc == NULL || strSub == NULL)//保证字符串的有效性         return -1;    while (strSrc){          bp = strSrc;//得到其字符串的首地址，从首地址开始进行逐一比较字符串是否相等！           sp = strSub;          do{              if (!*sp)//如果子串到达了字符串的结束符，证明已经找到，返回其位置                 return pos;           } while (*bp++ == *sp++);          pos++;          strSrc++;//如果没有找到，将主模式串的位置向前推进一位，继续比较，一直到达字符串的结尾！     }     return -1; } int main(){    char *strSrc = "123456";    char *strSub = "345";    int pos = mystrstr(strSrc, strSub);    cout << pos << endl;         system("pause"); } *///strrev函数的实现 #include <iostream>#include <cstdio>using namespace std;//方法1：遍历字符串，将第一个字符和最后一个字符交换，第2个和倒数第2个字符交换，依次循环！ char *strrev1(const char* str){     int len = strlen(str);     char *tmp = new char[len+1];     strcpy(tmp, str);     for (int i = 0; i < len/2; i++){         char c = tmp[i];         tmp[i] = tmp[len-1-i];         tmp[len-1-i] = c;      }           return tmp; } //方法2：用指针进行直接的操作char *strrev2(const char *str){     int len = strlen(str);     char *tmp = new char[len+1];     strcpy(tmp, str);     char *ret = tmp;//保存首地址      char *p = tmp + len - 1; //保存尾地址          while (p > tmp){           char t = *tmp;           *tmp = *p;           *p = t;           --p;           ++tmp;      }           return ret; } //方法3：我们借助异或运算（^）完成两个字符的交换char *strrev3(const char *str){     char *tmp = new char[strlen(str) + 1];     strcpy(tmp, str);     char *ret = tmp;     char *p = tmp + strlen(str)-1;          while (p > tmp){           *p ^= *tmp;           *tmp ^= *p;           *p ^= *tmp;           --p;           ++tmp;      }           return ret; } char *strrev4(const char *str){     char *tmp = new char[strlen(str) + 1];     strcpy(tmp, str);     char *ret = tmp;     char *p = tmp + strlen(str)-1;          while (p > tmp){           *p = *p + *tmp;           *tmp = *p - *tmp;           *p = *p - *tmp;           --p;           ++tmp;      }           return ret; } int main(){    char *str = "123456";    cout << str << endl;        char *str2 = strrev1(str);    cout << str2 << endl;        char *str3 = strrev2(str);    cout << str3 << endl;        char *str4 = strrev3(str);    cout << str4 << endl;        char *str5 = strrev4(str);    cout << str5 << endl;        system("pause"); }