函数strncpy，strncat，strncmp的使用以及模拟实现

strncpy模拟实现strncpy strncat模拟实现strncat strncmp模拟实现strncmp

strncpy

拷贝num个字符从源字符串到目标空间

如果源字符串的长度小于num，则拷贝完源字符串之后，在目标的后边追加0，直到num个

int main(){char arr[] = "xxxxxxxx";char arr1[] = "abcdef";strncpy(arr, arr1, 7);printf("%s\n", arr);return 0;}

模拟实现strncpy

char* my_strncpy(char* des, const char* src, size_t num){assert(des && src);char* ps = des;while (num--){//防止指针越界if (*src == '\0'){*des++ = '\0';}else*des++ = *src++;}return ps;}int main(){char arr[] = "xxxxxxxx";char arr1[] = "abcdef";my_strncpy(arr, arr1, 7);printf("%s\n", arr);return 0;}

strncat

追加num个字符，从源字符串到目标字符串，追加之后会给目标字符串补个’\0’

如果源字符串的长度小于num，则追加完源字符串之后，只会补一个’\0’

int main(){char arr[20] = "hello ";char arr1[] = "world";strncat(arr, arr1, 7);printf("%s\n", arr);return 0;}

模拟实现strncat

char* my_strncat(char* des, const char* src, size_t num){assert(des && src);char* ps = des;while (*des){des++;}while (*des++ = *src++);*des = '\0';return ps;}int main(){char arr[20] = "hello ";char arr1[] = "world";my_strncat(arr, arr1, 7);printf("%s\n", arr);return 0;}

strncmp

比较到出现到字符不一样或者一个字符串结束或者num个字符串全部比较完

模拟实现strncmp

int my_strcmp(const char* des, const char* src,size_t num){assert(des && src);while (num--){if (*des == *src){if (*des == '\0')return 0;des++;src++;}else if(*des > *src){return 1;}else{return -1;}}}int main(){char arr[] = "abbedf";char arr1[] = "abc";int ret=strncmp(arr, arr1,4);if (ret > 0)printf(">\n");else if (ret < 0)printf("<\n");elseprintf("==\n");return 0;}