C常用库函数实现

void *memcpy(void* dest, const void* src, size_t n)
{
    assert(dest != NULL && src != NULL && n > 0);

    if ((src < dest) && ((char*)src + n > dest)) {
        char* d = (char*)dest+n-1;
        char* s = (char*)src+n-1;

        while (n--) {
            *d-- = *s--;
        }
    } else {
        char* d = (char*)dest;
        char* s = (char*)src;

        while (n--) {
            *d++ = *s++;
        }
    }
    return dest;
}
// unsafe function
void *memcpy(void *dest, const void *src, size_t count)
{
    if(dest == NULL || src == NULL || count <= 0)  return NULL;
    char *d = (char *)dest;
    char *s = (char *)src;
    while(count--)
    {
        *d = *s;
		d++;
		s++;
    }
    return dest;
}

void *memmove(void *dest, const void *src, size_t count)
{
    if(dest == NULL || src == NULL || count <= 0)  return NULL;

    if(dest < src)
    {
        char *d = (char *)dest;
        char *s = (char *)src;
        while (count--)
        {
            *d++ = *s++;
        }
    }
    else
    {
        char *d = (char *)dest + count;
        char *s = (char *)src + count;
        while (count--)
        {
            *--d = *--s;
        }
    }
    return dest;
}

void* memset(void* src, int c, size_t n)
{
    assert((src != NULL) && (n > 0));

    char* psrc = (char*)src;

    while (n--)
	{
        *psrc++ = (char)c;
    }
    return src;
}

// unsafe function
char* strcpy(char *dest, char *src)
{
    if(dest == NULL || src == NULL)
        return NULL;

    char *res = dest;
    while(*src != '\0')
    {
        *dest = *src;
        dest++;
        src++;
    }
    *dest = '\0';
    return res;
}

// n <= strlen(dest)
char* strncpy(char* dest, const char* src, size_t n)
{
    assert(dest != NULL && src != NULL && n > 0);
	char *pdst = dest;

    if (src < dest && src + n > dest) { // strlen(src) > strlen(dest), copy first n of src to dest
        pdst = dest + n - 1;
        src = src + n -1;

        while (n) {
            *pdst-- = *src--;
			n--;
        }
    } else {
		while (*src && n) {
			*pdst++ = *src++;
			n--;
		}
		while (n--) {
			*pdst++ = '\0';
		}
    }

    return dest;
}

char *strcat(char *dest, char *src)
{
	assert(dest != NULL && src != NULL);

    char *head = dest;

    while (*dest != '\0') {
        dest++;
	}

    while (*src != '\0') {
        *dest = *src;
        dest++;
        src++;
    }

    *dest = '\0';

    return head;
}

int strcmp(const char* s1,const char* s2)
{
    assert(s1 != NULL && s2 != NULL);

    while (s1 && s2 && *s1 == *s2) {
        s1++;
        s2++;
    }
    return *s1 - *s2;
}

size_t strlen(const char *str)
{
    assert(str != NULL);

    int num = 0;
    while(*str != '\0')
    {
        str++;
        num++;
    }
    return num;
}

const char* strstr(const char *str1, const char *str2)
{
    if (str1== NULL || str2 == NULL) {
        return NULL;
	}

    const char *temp = str1;
    const char *res = str2;

	while (*str1 != '\0') {
        temp = str1;
        res = str2;
        while (*temp== *res) {
            temp++;
            res++;
        }
        if (*res == '\0') {
			return str1;
		}
        str1++;

    }

    return NULL;
}

char* strchr(const char* s, int c)
{
    if (NULL == s) {
        return NULL;
    }

	do {
		if (*s == ((char)c)) {
			return (char *)s;
		}
	} while (*s++);

	return NULL;
}

char* strdup(char *src)
{
    if (NULL == src) {
        return NULL;
    }
    char *p_src = src;
    int count = 0 ;

    while (*p_src != '\0') {
         count++;
         p_src++;
    }

    char *new_addr  = (char *)malloc(sizeof(char) * (count + 1));
	if (new_addr == NULL) {
		return NULL;
	}

    p_src = src;
    while (*p_src != '\0') {
        *new_addr++ = *p_src++;
    }
    *new_addr = '\0';
    return (new_addr -(count));
}

int isspace(int x)
{
    if (x == ' ' || x == '\t' || x == '\n' || x =='\f' || x =='\b' || x == '\r')
        return 1;
    else
        return 0;
}

int atoi(const char* nptr)
{
    int ret;
    int sign;

    while (isspace((int)(unsigned char)*nptr))
	{
		++nptr;
	}

	if ((*nptr == '-') || (*nptr == '+'))
	{
		sign = *nptr;
		nptr++;
	}
	else
	{
		sign = '+';
	}

    ret = 0;
    while ((*nptr <= '9') && (*nptr >= '0'))
    {
        ret = 10 * ret + (*nptr - '0');
        nptr++;
    }

    if (sign == '-')
        return -ret;
    else
        return ret;
}



Safe C Library

Gitee 极速下载 / safeclib;
GIthub safeclib;
Safe C Library;

### C语言常用库函数实现方法 #### asctime 函数实现 `asctime` 函数用于将 `struct tm` 类型的时间数据转换成字符串表示形式。此函数返回一个指向静态字符数组的指针,该数组包含了以特定格式表示的时间和日期。 ```c char* my_asctime(const struct tm *timeptr) { static char wday_name[7][4] = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"}; static char mon_name[12][4] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"}; static char result[26]; snprintf(result, sizeof(result), "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n", wday_name[timeptr->tm_wday], mon_name[timeptr->tm_mon], timeptr->tm_mday, timeptr->tm_hour, timeptr->tm_min, timeptr->tm_sec, 1900 + timeptr->tm_year); return result; }[^2] ``` #### strncmp 函数实现 `strncmp` 函数比较两个字符串前 n 个字节的内容。如果这两个字符串相等,则返回零;如果不相等则返回它们第一个不同之处所对应的 ASCII 差值。 ```c int my_strncmp(const char *cs, const char *ct, size_t n) { while (n--) { if (*cs != *ct) return *(unsigned char *) cs - *(unsigned char *) ct; if (*cs == '\0') break; cs++; ct++; } return 0; }[^4] ``` #### pow 函数实现 `pow` 函数用来求解给定底数 x 的 y 次方的结果。这个操作通常通过指数运算来完成,在这里提供了一个简单的迭代版本而非标准库中的高效算法。 ```c double my_pow(double base, int exponent) { double result = 1.0; for(int i=0;i<exponent;++i){ result *=base ; } return result; } // 注意:上述代码仅适用于正整数指数的情况。对于负数或非整数情况需进一步完善。 // 此外,实际应用中应考虑数值范围溢出等问题。[^3]
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