c語(yǔ)言string.h頭文件字符串檢驗(yàn)函數(shù)仿寫
所需頭文件：stdio.h ,stdlib.h, string.h
strlen字符串求長(zhǎng)度
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int strlen_my(const char* src_str){ if (NULL == src_str) { return -1; } const char* p = src_str; while (*p != '\0') { p++; } return p - &(src_str[0]);}//遞歸int strlen_my2(const char* src_str){ if (src_str == NULL) return -1; if (*src_str) { return strlen_my2(src_str + 1) + 1; } else { return 0; }} int main(){ const char* p = "hello"; printf("%d \n",strlen_my(p)); return 0;} |
strcmp / strncmp字符串比較
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int strcmp_my(const char* str_a, const char* str_b){ while ((*str_a != '\0' || *str_b != '\0') && *str_a == *str_b ) { str_a++; str_b++; } return *str_a - *str_b > 0 ? 1 : (*str_a - * str_b < 0 ? -1 : 0);}int strcmp_my2(const char* str_a, const char* str_b){ int sub = 0; while ((sub = *str_a - *str_b) == 0 && *str_a++ && *str_b++); //先賦值，指針再++ return sub > 0 ? 1 : (sub < 0 ? -1 : 0);} int strncmp_my(const char* str_a, const char* str_b, size_t front_len){ while (--front_len && *str_a != '\0' && *str_b != '\0' && *str_a == *str_b) { str_a++; str_b++; } return *str_a - *str_b > 0 ? 1 : (*str_a - *str_b < 0 ? -1 : 0);} int main(){ const char* p = "hella"; const char* q = "hell"; printf("%d \n", strncmp_my(p, q, 4)); return 0;} |
strchr / strrchr 字符串中查找字符ch
第一個(gè)出現(xiàn)的字符ch
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//strchr 返回字符串中第一個(gè)出現(xiàn)的字符chchar* strchr_my(const char* src_str, char ch){ if (src_str == NULL) { return NULL; } while (*src_str != '\0' && *src_str != ch) { src_str++; } return *src_str == '\0' ? NULL : src_str;} int main(){ const char* p = "hello"; p = strchr_my(p, 'e'); if (p == NULL) return 0; printf("%c\n", *p);} |
最后一個(gè)出現(xiàn)的字符ch
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//strrchr查找字符串中最后一個(gè)出現(xiàn)的字母chchar* strrchr_my(const char* src_str, char ch){ if (NULL == src_str) return NULL; const char* p = src_str + strlen(src_str) - 1; while ((p - src_str) >= 0 && *p != ch) { p--; } if (p - src_str == -1) { return NULL; } return p;} int main(){ const char* p = "hello"; //p = strchr_my(p, 'q'); p = strrchr_my(p, 'l'); if (p == NULL) return 0; printf("%c\n", *p);} |
strstr 字符串匹配：src_str中查找des_str，返回匹配的起始位置，沒(méi)有為NULL（BF算法）
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char* strstr_my(const char* src_str, const char* des_str){ if (NULL == src_str || NULL == des_str) { return NULL; } int len_src = strlen(src_str); int len_des = strlen(des_str); int i = 0; //src_str int j = 0; //des_str while (i < len_src && j < len_des) { if (src_str[i] == des_str[j]) { i++; j++; } else { i = i - j + 1; j = 0; } } if (j == len_des) { return src_str + i - j; } return NULL;} int main(){ const char* p = "hello"; const char* q = "llo"; const char* rt = strstr_my(p, q); if (rt != NULL) { printf("%s\n", rt); return 0; } return 0;} |
strcpy / strncpy字符串拷貝
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char* strcpy_my(char* des_str, const char* src_str){ if (des_str == NULL || src_str == NULL) return NULL; char* p = des_str; while (*src_str != '\0') { *p++ = *src_str++; } *p = '\0'; return des_str;} char* strncpy_my(char* des_str, const char* src_str, size_t len){ if (des_str == NULL || src_str == NULL || len <= 0) return NULL; char* p = des_str; //源字符串實(shí)際長(zhǎng)度 int cur_len = strlen(src_str) <= len ? len : strlen(src_str); while (cur_len--) { *p++ = *src_str++; } *p = '\0'; return des_str;} int main(){ const char* p = "hello"; char q[10] = {0}; if (strncpy_my(q, p, 1) != NULL) { printf("%s\n", q); } return 0;} |
strcat / strncat字符串的粘貼
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char* strcat_my(char* des_str, const char* src_str){ if (des_str == NULL || src_str == NULL) return NULL; int len_des = strlen(des_str); char* p = des_str + len_des; while (*src_str != '\0') { *p++ = *src_str++; } return des_str;} char* strncat_my(char* des_str, const char* src_str, size_t len){ if (des_str == NULL || src_str == NULL || len < 0) return NULL; int len_des = strlen(des_str); char* p = des_str + len_des; while (len--) { *p++ = *src_str++; } return des_str;} int main(){ char p[20] = "hello"; const char* q = "world"; printf("p = %s\n", p); printf("q = %s\n", q); if (strncat_my(p, q, 3) != NULL) { printf("p = %s\n", p); } printf("q = %s\n", q); return 0;} |
strdup 字符串申請(qǐng)堆區(qū)空間存放字符串的副本
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char* strdup_my(const char* src_str){ if (NULL == src_str) return NULL; char* newspace = (char*)malloc((strlen(src_str) + 1 ) * sizeof(char)); if (newspace == NULL) return NULL; int i = 0; while (*src_str != '\0') { newspace[i++] = *src_str++; } newspace[i] = '\0'; return newspace;}int main(){ const char* p = "hello"; char* q = strdup_my(p); if (q != NULL) { printf("%s\n", q); free(q); q == NULL; } return 0;} |
總結(jié)
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原文鏈接：https://blog.csdn.net/xiaoxiaoguailou/article/details/121267391
