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C Program with Pointer Increment False Values


C Program with Pointer Increment False Values

By : George Lopez
Date : November 21 2020, 11:01 PM
This might help you In order to make your code compile, I had to make one change: I added 'int' before 'main', so that the main function could correctly return 0.
The problem is that you have created an integer array of size 4, but you want it to contain 5 items.
code :
int numar[4];
numar[0]
numar[1]
numar[2]
numar[3]
numar[4]
int numar[5];
array[0] is at address 0x7fff557f0730 with value 0
array[1] is at address 0x7fff557f0734 with value 1
array[2] is at address 0x7fff557f0738 with value 2
array[3] is at address 0x7fff557f073c with value 3
array[4] is at address 0x7fff557f0740 with value 4


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How come I don't have to increment an array pointer whilst allocating values to it

How come I don't have to increment an array pointer whilst allocating values to it


By : FRFDNPG
Date : March 29 2020, 07:55 AM
Any of those help Well, you don't have to do anything. In your code, you don't initialize the whole array - you just assign 100 different values to its first member. Your code is just like:
code :
double d;
for(i=0;i<100;i++){
            d=j++;
            printf(" %0.1lf\n",d);
}
double *temp=ptr;
for(i=0;i<100;i++){
            *temp=j++;
            printf(" %0.1lf\n",*temp++);
}
Output of C program involving pre/post increment and pointer

Output of C program involving pre/post increment and pointer


By : user3655469
Date : March 29 2020, 07:55 AM
around this issue I was a solving guess output of following C code quiz, where I didnt get the output of below one:
code :
*ptr++
(*ptr)++
*ptr
*++ptr
++*ptr
Why does my program crash when I increment a pointer and then delete it?

Why does my program crash when I increment a pointer and then delete it?


By : Hek
Date : March 29 2020, 07:55 AM
it should still fix some issue It's actually the statement after the one you mark as causing the program to crash that causes the program to crash!
You must pass the same pointer to delete[] as you get back from new[].
C++ pre-increment vs post-increment on char* pointer while assigning a value

C++ pre-increment vs post-increment on char* pointer while assigning a value


By : 远 思
Date : March 29 2020, 07:55 AM
wish helps you First, pre-increment is only potentially faster for the reason you state. But for basic types like pointers, in practice that's not the case, because the compiler can generate optimized code. Ref. Is there a performance difference between i++ and ++i in C++? for more details.
Second, to a decent optimizing compiler, there's no difference between the two alternatives you mentioned. It's very likely the same exact machine code will be generated for both cases (unless you disabled optimizations).
code :
# c = *temp++;
movq    temp(%rip), %rax
leaq    1(%rax), %rdx
movq    %rdx, temp(%rip)
movzbl  (%rax), %eax
movb    %al, c(%rip)

# c = *temp;
movq    temp(%rip), %rax
movzbl  (%rax), %eax
movb    %al, c(%rip)
# ++temp;
movq    temp(%rip), %rax
addq    $1, %rax
movq    %rax, temp(%rip)
# c = *temp++;
movq    temp(%rip), %rax
leaq    1(%rax), %rdx
movq    %rdx, temp(%rip)
movzbl  (%rax), %eax
movb    %al, c(%rip)

# c = *temp;
# ++temp;
movq    temp(%rip), %rax
movzbl  (%rax), %edx
addq    $1, %rax
movq    %rax, temp(%rip)
movb    %dl, c(%rip)
Why can a pointer not point to post increment but can do that to pre increment?

Why can a pointer not point to post increment but can do that to pre increment?


By : Mahesh V Shet CP QA-
Date : March 29 2020, 07:55 AM
should help you out The problem here is not the pointers. It's the action of taking addresses of variables (on the RHS of the assignment operations).
The operator & can only be used on lvalues. When you post-increment a variable, the value of the expression is an rvalue, which is not eligible to be taken address.
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