面試-編程【1】-常見函數彙總

秋招已經接近尾聲，現將自己面試中遇到的題目進行彙總和分享

 

1. void *mymemcpy(void *dest, const void* src, size_t n)；

void* memcpy(void* dest,void* src,size_t n)
{
    assert(dest != NULL && src != NULL);
    if(src < dest && (char*)src + n > dest)
    {
        char* pdst = (char*)dest+n-1;
        char* psrc = (char*)src+n-1;
        while(n--)
        {
            *pdst-- = *psrc--;
        }
    }
    else
    {
        char* pdest = (char*)dest;
        char* psrc = (char*)src;
        while(n--)
        {
            *pdest++ = *psrc++;
        }
    }
    return dest;
}

 2.void *memset(void *s, int c, size_t n);

 

void* memset(void* src,int c,size_t n){
    assert(src != NULL);
    char* psrc = (char*)src;
    while(n--)
    {
        *psrc++ = (char)c;
    }
    return src;
}

3. char* strcpy(char* dest,const char* src);

 

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

    size_t n = strlen(src);
    if(src < dest && src + n > dest)
    {
        char* pdst = dest + n;
        *pdst-- = '\0';
        src = src + n - 1;
        while(n--)
        {
            *pdst-- = *src--;
        }
    }
    else
    {
        char* pdst = dest;
        while((*pdst++ = *src++) != '0');//這裏會一直複製到'\0'爲止
    }
    return dest;
}

4. char* mystrncpy(char* dest,char* src,size_t n);

 

char* strncpy(char* dest,const char* src,size_t n){
    assert(dest != NULL && src != NULL);

    if(src < dest && src + n > dest)
    {
        int m = strlen(src) < n ? strlen(src):n;
        char* pdst = dest+m;
        *pdst-- = '\0';
        src = src + m-1;
        while(m--)
        {
            *pdst-- = *src--;
        }
    }
    else
    {
        char* pdst = dest;
        size_t i = 0;
        while(i++ < n && (*pdst++ = *src++) != '\0');
        if(*(pdst-1) != '\0') *pdst = '\0';
    }
    return dest;
}

5.char* strcat(char* dest,const char* src)

 

char* strcat(char* dest,const char* src)
{
    assert(dest != NULL && src != NULL);
    char* pdst = dest;
    while(*pdst != '\0')
    {
        pdst++;
    }
    while((*pdst++ = *src++) != '\0');
    return dest;
}

6.int strcmp(const char* s1,const char* s2)

int strcmp(const char* s1,const char* s2){
    assert(s1 != NULL && s2 != NULL);
    while(s1 && s2 && *s1 == *s2){
        s1++;
        s2++;
    }
    return *s1 - *s2;
}

7.size_t strlen(const char* s)

size_t strlen(const char* src){
    assert(src != NULL);
    size_t ret = 0;
    while(*src++ != '\0'){
        ret++;
    }
    return ret;
}

二分查找

 

int binary_search(int* arr, int key, int n)
 {
    int low=0;
    int mid;
    int high=n-1;
    while(low<=high)
    {
        mid = (low+high)/2;
        if(key < arr[mid])
        {
            high=mid-1;
        }
        else if(key>arr[mid])
        {
            low=mid+1;
        }
        else
        {
            return mid;
        }
    }
    return -1;
 }
 
int main(int argc, char *argv[])
{
    if(1)
    {
        int it[] = {0,1,2,3,4,5,6,7};
        int index = binary_search(it, 7, 8);
        printf("index=%d\n", index); //index=7
    }
 
    return 0;
}