About the size mismatch problem and the array value change problem when the strcpy () function is copying a string array

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The source of the problem is a test code that you write yourself:

#include <iostream>using namespacestd;intMain () {Chara[1]; a[0] ='a'; a[1] ='b'; Charb[1]; b[0] ='C'; b[1] ='D';    strcpy (A, b); cout<<"after copy: a[0] ="<<a[0]<<"a[1] ="<<a[1]<<Endl; cout<<"after copy: b[0] ="<<b[0]<<"b[1] ="<<b[1]<<Endl; return 0;}

After that, the value of the two string output is not imaginary:

"After copy: a[0] = c A[1] = d

After copy: b[0] = c B[1] = d "

But:

When I first saw the face, why did I use strcpy () after the copy, the value of the source character array is not correct?

So I wrote some test output code, and display the two-character array header in the memory location of the output code to find out where the problem lies:

#include <iostream>using namespacestd;intMain () {Chara[1]; a[0] ='a'; a[1] ='b'; cout<<"A[0] ="<<a[0]<<"a[1] ="<<a[1]<<Endl; Charb[1]; b[0] ='C'; b[1] ='D'; cout<<"declaration Char b[1] After: a[0] ="<<a[0]<<"a[1] ="<<a[1]<<Endl; cout<<"B[0] ="<<b[0]<<"b[1] ="<<b[1]<<Endl;    strcpy (A, b); printf ("%x\n", a); printf ("%x\n", B); cout<<"after copy: a[0] ="<<a[0]<<"a[1] ="<<a[1]<<Endl; cout<<"after copy: b[0] ="<<b[0]<<"b[1] ="<<b[1]<<Endl; return 0;}

The following output is then obtained:

As you can see, the value in the character array A has been changed since the end of the statement Char B[1] this little hooker!

What is this for?

As you can see, the addresses of thetwo character arrays, A and B, differ by only 1, which is where the problem lies!

At the end of the declaration of Char A[1], this is the case in memory:

53151adb ' a '//here is the start address of the character array a

53151ADC ' B '

53151add ' + '

When the Char b[1] is declared, the memory becomes:

53151ada ' C '//Here is the start address of the character array B

53151adb ' d '//Here is the start address of the character array A, the original ' A ' is covered by the ' d ' in the character array B!

53151ADC ' + '//original ' B ' is covered by the end character in array b

53151add ' + '

This explains why A[1] became a ' d ' problem when the Char b[1] was declared.

So what happens when we use strcpy (A, b)?

This function copies the values in B to a in a, so the memory address grows after the copy is done:

53151ada ' C '//Here is the start address of the character array B

53151adb ' C '//Here is the start address of the character array A, just ' d ' is covered by the ' C ' in the character array B!

53151ADC ' d '//just ' s ' is covered by ' d ' in the character array B!

53151add ' + '

At this time, the output of the character array A and B when the beginning of the show we saw a lump of &%&%￥%@ ... Well.

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About the size mismatch problem and the array value change problem when the strcpy () function is copying a string array