str.c

#include <assert.h>
#include <iconv.h>
#include <locale.h>
#include <stdio.h>
#include <string.h>
#include <wchar.h> //unicode utf-8

void *my_memcpy(void *dest, void *src, unsigned count) {
  if (dest == NULL || src == NULL) {
    return NULL;
  }
  char *pdest = (char *)dest;
  char *psrc = (char *)src;
  while (count--) {
    *pdest++ = *psrc++;
  }
  return dest;
}

char *my_strchr(const char *s, int c) {
  printf("%c,%d\n", c, c);
  if (s == NULL) {
    return NULL;
  }
  while (*s != '\0') {
    if (*s == (char)c) {
      return (char *)s;
    }
    s++;
  }
  return NULL;
}

char *stpcpy23(char *dest, const char *src) {
  size_t len = strlen(src);
  return memcpy(dest, src, len + 1) + len;
}
int my_strlen(const char *str) {
  assert(str);
  int count = 0;
  while (*str) {
    count++;
    str++;
  }
  return count;
}

size_t my_strlen2(const char *str) {
  const char *end = str;
  while (*end++)
    ;
  return end - str - 1;
}
// #define BITOP(a,b,op) \
//  ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))

// size_t strcspn1(const char *s, const char *c) {
// 	const char *a = s;
// 	size_t byteset[32/sizeof(size_t)];
// 	if (!c[0] || !c[1]) return __strchrnul(s, *c)-a;
// 	memset(byteset, 0, sizeof byteset);
// 	for (; *c && BITOP(byteset, *(unsigned char *)c, |=); c++);
// 	for (; *s && !BITOP(byteset, *(unsigned char *)s, &); s++);
// 	return s-a;
// }

char *strpbrk1(const char *s, const char *b) {
  s += strcspn(s, b);
  return *s ? (char *)s : 0;
}

// 二级指针传参 练习
int sq(char **num) {
  *num = "feng";
  return 2;
}
void feng() {
  char *one = "a";
  sq(&one);
  printf("c: %s \n", one);
}
int sq1(char *num) {
  printf("ca: %s \n", num);
  num = "feng";
  return 2;
}
void feng1() {
  char *one = "a";
  sq1(one);
  printf("c: %s \n", one);
}

void cm(char *p, int num) { p = (char *)malloc(sizeof(char) * num); }
void cm2(char **p, int num) {
  // p = (char *)malloc(sizeof(char)*num); //不会报错.
  *p = (char *)malloc(sizeof(char) * num);
}

// http://c.biancheng.net/c/assert/
// 在操作指针时，一定要保证在指针有效内存空间内操作,不然 Segmentation fault
// 段错误。 被操作系统kill. c编译器内置宏 https://zhuanlan.zhihu.com/p/409044316
int main(void) {
  // assert(NULL);
  printf("文件: %s,函数: %s %s %s \n", __FILE__, __func__, __ASSERT_FUNCTION,
         __DATE__); //几个c编译器内置变量
  char destination[25];
  char *blank = " ", *c = "C++", *Borland = "Borland";

  strcpy(destination, Borland);
  strcat(destination, blank);
  strcat(destination, c);

  printf("is: %s\n", strchr(destination, 'a'));
  printf("is2: %s\n", my_strchr(destination, 'a+lskjdsafsfsfa'));
  printf("%s\n", destination);

  // 字符串分割
  char str[80] = "This is - www.runoob.com - website";
  // const char s[2] = "-";
  char *s = "-";
  char *token;
  /* 获取第一个子字符串 */
  token = strtok(str, s);
  /* 继续获取其他的子字符串 */
  while (token != NULL) {
    printf("%s\n", token);
    token = strtok(NULL, s);
  }
  //调用 strcat 必须保证目标地址有足够的已分配的内存用于存储结果。通常需要用
  //malloc 提前分配内存 或 定义一个足够大的静态 char[] 。
  // char* one1="hao",one2=" ca";
  char one1[100] = "hao";
  // char *one1=malloc(100);
  char *one2 = " ca";
  printf("strcat: %s \n", strcat(one1, one2));
  printf("%d \n", strlen("wanglaowu"));
  printf("%d \n", strlen("行者")); // strlen 计算的是字节 不是字符。
  printf("%d \n", wcslen("行者")); // strlen 计算的是字节 不是字符。

  static char *const terminating_characters = " ,[](){};\n";
  const char *identifier = "fen[g (+ 3 2)";
  char *end = strpbrk(identifier, terminating_characters);
  printf("strpbrk: %s \n", end);
  feng1();
  feng();
  // char* str1 = NULL;
  char *str1 = "hao";
  printf("addr1: %p \n", &str1);
  printf("addr1: %p \n", str1);
  cm(&str1, 20);
  printf("addr2: %p \n", str1);
  // printf("addr3: %p \n",&str1);
  // cm2(str1, 20); //报错...
  // printf("addr3: %p \n",str1);
  cm2(&str1, 20);
  printf("addr4: %p \n", str1);
  int *a1 = 12;
  *a1 = 88;
  printf("%p, %d\n", a1, *a1);
  return 0;
}
// gcc str.c  && ./a.out