A program, always paragraph error, hope you can help me to see where there is a problem?
-sharpinclude <stdio.h>
-sharpinclude <stdlib.h>
-sharpinclude <string.h>
int getmax(int a, int b)
{
if(a>b)
{
return a;
}else
{
return b;
}
}
void swap(void * a, void * b)
{
void * tmp;
int la=sizeof(a);
int lb=sizeof(b);
int max=getmax(la,lb);
void * t=(void *)malloc(max);
if(t ==NULL)
{
printf("%s\n","");
exit(0);
}
memcpy(t,a,max);
memcpy(a,b,max);
memcpy(b,t,max);
printf("%d\n",sizeof(a));
printf("%d\n",sizeof(b));
printf("%d\n",max);
free(t);
}
int main()
{
char * str="123";
char * str2="456";
swap((void *)str,(void *)str2);
printf("%s\n",str);
printf("%s\n",str2);
}
char * str="123";
char * str2="456";
the two strings requested in this way are actually two pointers str and str2 pointing to two string constants respectively.
so when you execute this code:
memcpy(a,b,max);
memcpy(b,t,max);
will report an error because you are trying to modify the string constant.
< hr >
in addition, if you give two strings of different length, your program will also make mistakes. This is left to you to think about and solve
.
if you just want to compile and pass, you can make the following changes:
char * str="123";
char * str2="456";
modify to
char str1[]="123";
char str2[]="456";
secondly, memcpy should not use max, twice when copying. You should use lb, once and la once. Do you want to check their sizes before memcpy, such as char str1 [3] = "12" str2 [4] = "123", so there is a problem with the exchange?
there must be a lot of things that haven't been taken into account.
this is my modified program, which is running normally for the time being.
-sharpinclude <stdio.h>
-sharpinclude <stdlib.h>
-sharpinclude <string.h>
-sharpinclude <assert.h>
int getmax(int a, int b)
{
if(a>b)
{
return a;
}else
{
return b;
}
}
void swap(void * a, void * b,int la, int lb)
{
void * tmp;
int max=getmax(la,lb);
void * t=(void *)malloc(max);
if(t == NULL)
{
printf("%s\n","");
exit(0);
}
memcpy(t,a,max);
memcpy(a,b,max);
memcpy(b,t,max);
free(t);
}
int main()
{
char str[]="123456789";
char str2[]="abcd";
printf("%s\n",(char *)str);
printf("%s\n",(char *)str2);
swap((void *)str,(void *)str2, sizeof(str), sizeof(str2));
printf("%s\n",(char *)str);
printf("%s\n",(char *)str2);
}
