一篇文章教你自己动手实现C语言库函数

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#include <stdio.h>

#include <string.h>

#include <assert.h>

//实现memmove

void* my_memmove(void* dst,constvoid* src,size_tn)

{

assert(dst && src);

char* dst_temp = (char*)dst;

char* src_temp = (char*)src;

if(src_temp<dst_temp && src_temp + n>dst_temp)//src在dst前，两者交错，需从后往前复制

{

while(n)

{

*(dst_temp + n - 1 )= *(src_temp + n - 1);

n--;

}

}

else

{

while(n--)

{

*dst_temp++ = *src_temp++;

}

}

returndst;

}

intmain()

{

inta[10] = { 0,1,2,3,4,5,6,7,8,9 };

my_memmove(a+2, a, 4*sizeof(int));

for(inti = 0; i < 10; ++i)

{

printf("%d ", a[i]);

}

return0;

}

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void*memcpy(void* destination,constvoid* source,size_tnum );

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//实现memcpy

void* my_memcpy(void* dst,constvoid* src,size_tn)

{

assert(dst && src);

char* dst_temp = (char*)dst;

char* src_temp = (char*)src;

while(n--)

{

*dst_temp++ = *src_temp++;

}

returndst;

}

intmain()

{

inta[10] = { 0,1,2,3,4,5,6,7,8,9 };

my_memcpy(a+2, a, 4*sizeof(int));

for(inti = 0; i < 10; ++i)

{

printf("%d ", a[i]);

}

return0;

}

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char*strstr(char* str1,constchar* str2 );

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/实现strstr

char* my_strstr(constchar* mom,constchar* son)

{

char* cp=mom;

char* i, *j;

if(*son =='\0')

{

returnmom;

}

while(*cp !='\0')

{

i = cp;

j = son;

while(i && *i == *j)

{

i++;

j++;

if(*j =='\0')

returncp;

}

cp++;

}

returnNULL;

}

intmain()

{

charmom[] ="abcdefghijk";

charson[] ="ghi";

printf("%s\n",my_strstr(mom, son));

return0;

}

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char* strstr (char* str1,constchar* str2 );