字符串

int main(int argc, const char * argv[]) {
    int ch;
    while((ch = getchar()) != EOF) {
        putchar(ch);
    }
    printf("EOF\n");
    return 0;
}
char a[][10] = {};
表示a[0] --> char [10]

char *a[] 
a[0] --> char *

$ln -s a.out my

$busybox

size_t strlen(const char *s);

size_t mylen(const char *s) {
    int cnt = 0;
    while(s[idx] != '\0') {
        idx++;
    }
    return idx;
}

int strcmp(const char *s1, const char *s2);

int mycmp(const char *s1, const char *s2) {
    for(int i = 0; i < strlen(s1); i++) {
        for (int j = 0; j < strlen(s2); j++) {
            if (s1[i] == s2[j]) {
                continue;
            }
            if (s1[i] > s2[j]) {
                return 1;
            }
            if (s1[i] < s2[j]) {
                return -1;
            }
        }
    }
    return 0;
}

int mycmp2(const char *s1, const char *s2) {
    //int idx = 0;
    //while(s1[idx] == s2[idx] && s1[idx] != '\0') {
    //  idx++;
    //}
    while (*s1 == *s2 && *s1 != '\0') {
        s1++; s2++;
    } 
    return *s1 - *s2;
    //return s1[idx] - s2[idx];
}


char *strcpy(char *restrict dst, const char *restrict src);
//restrict 表示dst和src不能重叠
//把src的内容拷贝到ds

char *dst = (char*)malloc(strlen(src)+1);
strcpy(dst,src);
char *mycpy(char * restrict dst, const char * restrict src) {
    int idx = 0;
//  while(src[idx] != '\0') {
//      dst[idx] = src[idx];
//      idx++;
//  }
//  dst[idx] = '\0';
    return dst;
    char *rest = dst;
    while(*dst++ = *src++) {
        NULL;
    }
    *dst = '\0';
    return rest;

} 
查找字符
char *strchr(const char *s, int c); // 左找
char *strrchr(const char *s, int c); // 右找
查找字符串
char *strstr(const char *s1, const char *s2);
char *strcasestr(const char *s1, const char *s2); //忽略大小写