c字符串函数及指针操作

C++的程序员对C中的字符串指针操作的函数却并不是相当的熟悉。而C中的这些字符串的指针操作函数有的时候也是必须要面对的，比如我们的库要提供C函数接口，保持向后兼容和跨平台，还有我们经常使用一些第三方的库中都或多或少的使用到了这些C中的指针操作函数，所以下面列出C的指针操作函数，帮助大家熟悉之。

1.模拟实现strncpy

char* my_strncpy(char*dest, const char*src, size_t n){assert(dest != NULL);assert(src != NULL);char* pdest = dest;int i = 0;for (i = 0; i < n; i++){*pdest++ = *src++;}return dest;}int main(){char arr1[10] = { 0 };char arr2[10] = "abcdef";my_strncpy(arr1, arr2, 2);printf("%s\n", arr1);system("pause:");return 0;}

2.模拟实现strncat

char *my_strncat(char *dest, const char *src, size_t n){char *ret = dest;assert(dest!=NULL);assert(src != NULL);while (*dest!='\0'){dest++;}while (n-- && (*src != '\0')){*dest++ = *src++;}return ret;}int main(){char str1[10] = "abcd";char str2[] = "efgh";my_strncat(str1, str2, 3);printf("%s\n", str1);system("pause:");return 0;}

3.模拟实现strncmp

char* my_strncmp(char*dest, const char*src, size_t n){int ret = 0;assert(dest != NULL);assert(src != NULL);while (n--){if (!(ret = *(unsigned char *)dest - *(unsigned char *)src)){dest++;src++;}}if (ret > 0)return 1;else if (ret<0)return -1;}int main(){char arr1[10] = "abcdef";char arr2[10] = "ab";printf("%d\n", my_strncmp(arr1, arr2, 3));system("pause:");return 0;}

4.模拟实现strchr

char* my_strchr(const char* arr, char ch){assert(arr);while (*arr != '\0'){if (*arr == ch){return arr;}arr++;}return NULL;}int main(){char arr[] = "abccd";printf("%s\n", my_strchr(arr, 'c'));system("pause");return 0;}

5.模拟实现strrchr

char* my_strrchr(char  const  *arr, char ch){char* pos = 0;assert(arr);while (*arr){if (*arr == ch){pos = arr;}arr++;}if (pos != 0)return pos;elsereturn NULL;}int main(){char arr[] = "abcccd";printf("%s\n", my_strrchr(arr, 'c'));system("pause");return 0;}