c/c++ 字符串函数（字符串函数的源代码）的实现strlen、strcpy、strcmp、strncmp、strcasecmp、strtok、strstr（面试题）

谁借莪１个温暖的怀抱￠ 2023-02-17 12:30 148阅读 0赞

# c/c++实现各种字符串函数的功能（字符串源码） #

//========================================
    //*author: ABNQ
    //*email:abnq_cn@qq.com
    //*create time :
    //*filename:my_str.c
    //*description:
    //========================================
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include "include.h"
    
    /*
    char *my_strcat(char *dest, const char *src);
    int  my_strcmp(const char *s1, const char *s2);
    int  my_strncmp(const char *s1, const char *s2, unsigned int n);
    int  my_strcasecmp(const char *s1, const char *s2);
    char *my_strcpy(char *dest, const char *src);
    char *my_strtok(char *str, const char *delim);
    char *my_strstr(const char *haystack, const char *needle);
    */
    char *my_strcat(char *dest, const char *src)
    { 
    	assert(dest != NULL && src != NULL);
    	char *tmp = dest;
    	
    	while(*dest != '\0'){ 
    		dest++;
    	}
    	
    	while((*dest++ = *src++) != '\0');
    	
    	return tmp;
    }
    
    int  my_strcmp(const char *s1, const char *s2){ 
    	assert(s1 != NULL && s2 != NULL);
    	
    	while (*s1 != '\0' && *s2 != '\0' && *s1 == *s2){ 
    		s1++;
    		s2++;
    	}
    	
    	return *s1 - *s2;
    }
    
    int  my_strncmp(const char *s1, const char *s2, unsigned int n){ 
    	assert(s1 != NULL && s2 != NULL);
    	
    	while(*s1 != '\0' && s2 != '\0' && *s1 == *s2 && --n){ 
    		s1++;
    		s2++;
    	}	
    	return *s1 - *s2;		
    }
    
    int my_strcasecmp(const char *s1, const char *s2){ 
    	assert(s1 != NULL && s2 != NULL);	
    
    	while(*s1 != '\0' && *s2 != '\0' &&
    				( ((*s1 >= 'A' && *s1 <= 'Z') ? (*s1 - 'A' + 'a') : (*s1)) == (( *s2 >= 'A' && *s2 <= 'Z') ? (*s2 - 'A' + 'a') :( *s2)))){ 
    		s1++;
    		s2++;
    	}
    	return ((*s1 >= 'A' && *s1 <= 'Z') ? (*s1 - 'A' + 'a') : (*s1))  - (( *s2 >= 'A' && *s2 <='Z') ? (*s2 - 'A' + 'a') :( *s2));	
    }
    
    char * my_strcpy(char *dest, const char *src){ 
    	assert(dest != NULL && src !=NULL);	
    		
    	char *tmp = dest;
    	while( ( *dest++ = *src++) != '\0');
    	return tmp;
    }
    
    char * my_strtok(char *str, const char *delim){ 
    	//assert(delim != NULL);
    
    	static char *last_str = NULL;
    	if(str == NULL && (str = last_str) == NULL){ 	//第一次使用my_strtok参数1为NULL的话，直接返回
    		return NULL;
    	}
    	char *tmp_str = str;
    	const char *tmp_delim = NULL;
    
    	while(*tmp_str != '\0'){ 
    		tmp_delim = delim;
    		while(*tmp_delim != '\0'){ 
    			if(*tmp_delim == *tmp_str){ 
    				last_str = tmp_str + 1;
    				if((int *) (tmp_str - str) == NULL){ 		//防止第一个是分隔符
    					str = last_str;
    					break;
    				}
    				*tmp_str = '\0';
    				return str;
    			}
    			tmp_delim++;
    		}
    		tmp_str++;
    	}
    	return str;			//到了字符串尾，返回最后一个分隔符地址加1
    }
    
    char *my_strstr(const char *haystack, const char *needle){ 
    	assert(haystack != NULL && needle != NULL);
    
    	char *tmp_haystack, *tmp_needle;
    	if(*needle == '\0'){ 
    		return (char *)haystack;
    	}
    	while(*haystack != '\0'){ 
    		tmp_haystack = (char *)haystack;
    		tmp_needle 	 = (char *)needle;
    		while(*tmp_haystack != '\0' && tmp_needle !='\0' && !(*tmp_haystack - *tmp_needle)){ 
    			tmp_haystack++;
    			tmp_needle++;
    		}
    		if(*tmp_needle == '\0'){ 
    			return tmp_haystack;
    		}
    		haystack++;
    	}
    	return NULL;
    }