INTERVIEW QUESTIONS C DYNAMIC MEMORY ALLOCATION IN C DETAILS

Question: what is the difference between the functions memmove() and memcpy()?

Answer:

Source: CoolInterview.com

MemCpy.

It copies count characters from the array pointed from source to destination. If the array overlaps the behaviour of memcpy is undefined.

Memmove

It copies count characters from the array pointed from source to destination. If the array overlaps the copy will take place correctly.

EX: char a[]="Hello World";
memmove(&a[2],"She",3);
prints "HeShe world"
memcpy(&a[2],"llo",3);
some times o/p is unexpected. Source: CoolInterview.com

both are same

memmove() and memcpy() copies specified number of characters from one buffer to another Source: CoolInterview.com

Its similar to typing without insert key ON and OFF
str1="strings are good");
memmove(str1+8,str1+11,4);
returns------ strings are are good
memcpy(str+8,str1+11,4)
returns------ strings are read


memcpy - just copies form source to destination.
memmove - copies from source to destination if buffers overlap ,every character is read before another character is written to the same location..


above example will give same output in both the cases as source and destination areas doesn't overlap also `are' will not be appended as claimed in above example.


instead use below example:


str = "0123456789"
memmove(str+2, str+1, 3);
returns: 0112356789

memcpy(str+2, str+1, 3);
returns: 0111356789


As we could see in second example of memcpy `1' is copied twice, from memory-location: 1 and then from memory-location:2 which was updated to `1' by memcpy, where as memmove uses a temporary buffer hence this problem didn't occur.
Source: CoolInterview.com

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