About the hexadecimal result of a-b, where each is a pointer to an array
1
I'm thinking about how the result of the following snippet is 0xc? Shouldn't it be c0-90=30? I run it on ideone.com.
#include <stdio.h>
int main(void) {
int a[10] = {0};
int b[10] = {0};
printf("sizeof(a) = %dn", (int)sizeof(a));
printf("%p, %pn", (void *)(a+10), (void *)(b+10));
printf("a = %p; b = %pn", (void *)a, (void *)b);
printf("a-b = %p", (void *)(a-b));
return 0;
}
Result:
sizeof(a) = 40
0x7ffcabb73ce8, 0x7ffcabb73cb8
a = 0x7ffcabb73cc0; b = 0x7ffcabb73c90
a-b = 0xc
c hex
asked Nov 21 '18 at 5:50
BinaryTreeeeBinaryTreeee
601324
add a comment |
1
I'm thinking about how the result of the following snippet is 0xc? Shouldn't it be c0-90=30? I run it on ideone.com.
#include <stdio.h>
int main(void) {
int a[10] = {0};
int b[10] = {0};
printf("sizeof(a) = %dn", (int)sizeof(a));
printf("%p, %pn", (void *)(a+10), (void *)(b+10));
printf("a = %p; b = %pn", (void *)a, (void *)b);
printf("a-b = %p", (void *)(a-b));
return 0;
}
Result:
sizeof(a) = 40
0x7ffcabb73ce8, 0x7ffcabb73cb8
a = 0x7ffcabb73cc0; b = 0x7ffcabb73c90
a-b = 0xc
c hex
asked Nov 21 '18 at 5:50
BinaryTreeeeBinaryTreeee
601324
It's clear from that output thata+10is the address of the tenthintaftera[0], which is 40 more thana. Unsurprisingly,(a + 10) - ais 10. Consider what that means forb - a(which is technically undefined behaviour, by the way).
– rici
Nov 21 '18 at 6:03
@rici: I thought that would be-(result)...
– BinaryTreeee
Nov 21 '18 at 6:11
add a comment |
1
1
1
I'm thinking about how the result of the following snippet is 0xc? Shouldn't it be c0-90=30? I run it on ideone.com.
#include <stdio.h>
int main(void) {
int a[10] = {0};
int b[10] = {0};
printf("sizeof(a) = %dn", (int)sizeof(a));
printf("%p, %pn", (void *)(a+10), (void *)(b+10));
printf("a = %p; b = %pn", (void *)a, (void *)b);
printf("a-b = %p", (void *)(a-b));
return 0;
}
Result:
sizeof(a) = 40
0x7ffcabb73ce8, 0x7ffcabb73cb8
a = 0x7ffcabb73cc0; b = 0x7ffcabb73c90
a-b = 0xc
c hex
asked Nov 21 '18 at 5:50
BinaryTreeeeBinaryTreeee
601324
I'm thinking about how the result of the following snippet is 0xc? Shouldn't it be c0-90=30? I run it on ideone.com.
#include <stdio.h>
int main(void) {
int a[10] = {0};
int b[10] = {0};
printf("sizeof(a) = %dn", (int)sizeof(a));
printf("%p, %pn", (void *)(a+10), (void *)(b+10));
printf("a = %p; b = %pn", (void *)a, (void *)b);
printf("a-b = %p", (void *)(a-b));
return 0;
}
Result:
sizeof(a) = 40
0x7ffcabb73ce8, 0x7ffcabb73cb8
a = 0x7ffcabb73cc0; b = 0x7ffcabb73c90
a-b = 0xc
c hex
c hex
asked Nov 21 '18 at 5:50
BinaryTreeeeBinaryTreeee
601324
asked Nov 21 '18 at 5:50
BinaryTreeeeBinaryTreeee
601324
asked Nov 21 '18 at 5:50
BinaryTreeeeBinaryTreeee
601324
asked Nov 21 '18 at 5:50
BinaryTreeeeBinaryTreeee
601324
asked Nov 21 '18 at 5:50
BinaryTreeeeBinaryTreeee
601324
601324
It's clear from that output thata+10is the address of the tenthintaftera[0], which is 40 more thana. Unsurprisingly,(a + 10) - ais 10. Consider what that means forb - a(which is technically undefined behaviour, by the way).
– rici
Nov 21 '18 at 6:03
@rici: I thought that would be-(result)...
– BinaryTreeee
Nov 21 '18 at 6:11
add a comment |
It's clear from that output thata+10is the address of the tenthintaftera[0], which is 40 more thana. Unsurprisingly,(a + 10) - ais 10. Consider what that means forb - a(which is technically undefined behaviour, by the way).
– rici
Nov 21 '18 at 6:03
@rici: I thought that would be-(result)...
– BinaryTreeee
Nov 21 '18 at 6:11
It's clear from that output that
a+10 is the address of the tenth int aftera[0], which is 40 more than a. Unsurprisingly, (a + 10) - a is 10. Consider what that means for b - a(which is technically undefined behaviour, by the way).– rici
Nov 21 '18 at 6:03
It's clear from that output that
a+10 is the address of the tenth int aftera[0], which is 40 more than a. Unsurprisingly, (a + 10) - a is 10. Consider what that means for b - a(which is technically undefined behaviour, by the way).– rici
Nov 21 '18 at 6:03
@rici: I thought that would be
-(result)...– BinaryTreeee
Nov 21 '18 at 6:11
@rici: I thought that would be
-(result)...– BinaryTreeee
Nov 21 '18 at 6:11
add a comment |
1 Answer
1
active
oldest
votes
2
When you subtract pointers you get the difference in locations not difference in bytes
So, you get 0x7ffcabb73cc0 - 0x7ffcabb73c90 = 0x30 bytes
Dividing this by 4 bytes per integer, you get 0x0c integers
answered Nov 21 '18 at 6:03
Rishikesh RajeRishikesh Raje
5,6171828
0x0c=12(decimal) so the compiler adds 2-integer distance between the start ofaand the end ofbright?
– BinaryTreeee
Nov 21 '18 at 6:09
2
@ptr_user7813604 - That is dependent on the compiler and/or memory and is not a requirement of the C language.
– Rishikesh Raje
Nov 21 '18 at 6:12
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
draft saved
draft discarded
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53405967%2fabout-the-hexadecimal-result-of-a-b-where-each-is-a-pointer-to-an-array%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
2
When you subtract pointers you get the difference in locations not difference in bytes
So, you get 0x7ffcabb73cc0 - 0x7ffcabb73c90 = 0x30 bytes
Dividing this by 4 bytes per integer, you get 0x0c integers
answered Nov 21 '18 at 6:03
Rishikesh RajeRishikesh Raje
5,6171828
0x0c=12(decimal) so the compiler adds 2-integer distance between the start ofaand the end ofbright?
– BinaryTreeee
Nov 21 '18 at 6:09
2
@ptr_user7813604 - That is dependent on the compiler and/or memory and is not a requirement of the C language.
– Rishikesh Raje
Nov 21 '18 at 6:12
add a comment |
2
When you subtract pointers you get the difference in locations not difference in bytes
So, you get 0x7ffcabb73cc0 - 0x7ffcabb73c90 = 0x30 bytes
Dividing this by 4 bytes per integer, you get 0x0c integers
answered Nov 21 '18 at 6:03
Rishikesh RajeRishikesh Raje
5,6171828
0x0c=12(decimal) so the compiler adds 2-integer distance between the start ofaand the end ofbright?
– BinaryTreeee
Nov 21 '18 at 6:09
2
@ptr_user7813604 - That is dependent on the compiler and/or memory and is not a requirement of the C language.
– Rishikesh Raje
Nov 21 '18 at 6:12
add a comment |
2
2
2
When you subtract pointers you get the difference in locations not difference in bytes
So, you get 0x7ffcabb73cc0 - 0x7ffcabb73c90 = 0x30 bytes
Dividing this by 4 bytes per integer, you get 0x0c integers
answered Nov 21 '18 at 6:03
Rishikesh RajeRishikesh Raje
5,6171828
When you subtract pointers you get the difference in locations not difference in bytes
So, you get 0x7ffcabb73cc0 - 0x7ffcabb73c90 = 0x30 bytes
Dividing this by 4 bytes per integer, you get 0x0c integers
answered Nov 21 '18 at 6:03
Rishikesh RajeRishikesh Raje
5,6171828
answered Nov 21 '18 at 6:03
Rishikesh RajeRishikesh Raje
5,6171828
answered Nov 21 '18 at 6:03
Rishikesh RajeRishikesh Raje
5,6171828
answered Nov 21 '18 at 6:03
Rishikesh RajeRishikesh Raje
5,6171828
5,6171828
0x0c=12(decimal) so the compiler adds 2-integer distance between the start ofaand the end ofbright?
– BinaryTreeee
Nov 21 '18 at 6:09
2
@ptr_user7813604 - That is dependent on the compiler and/or memory and is not a requirement of the C language.
– Rishikesh Raje
Nov 21 '18 at 6:12
add a comment |
0x0c=12(decimal) so the compiler adds 2-integer distance between the start ofaand the end ofbright?
– BinaryTreeee
Nov 21 '18 at 6:09
2
@ptr_user7813604 - That is dependent on the compiler and/or memory and is not a requirement of the C language.
– Rishikesh Raje
Nov 21 '18 at 6:12
0x0c = 12(decimal) so the compiler adds 2-integer distance between the start of a and the end of b right?– BinaryTreeee
Nov 21 '18 at 6:09
0x0c = 12(decimal) so the compiler adds 2-integer distance between the start of a and the end of b right?– BinaryTreeee
Nov 21 '18 at 6:09
2
2
@ptr_user7813604 - That is dependent on the compiler and/or memory and is not a requirement of the C language.
– Rishikesh Raje
Nov 21 '18 at 6:12
@ptr_user7813604 - That is dependent on the compiler and/or memory and is not a requirement of the C language.
– Rishikesh Raje
Nov 21 '18 at 6:12
add a comment |
draft saved
draft discarded
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
draft saved
draft discarded
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53405967%2fabout-the-hexadecimal-result-of-a-b-where-each-is-a-pointer-to-an-array%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
It's clear from that output that
a+10is the address of the tenthintaftera[0], which is 40 more thana. Unsurprisingly,(a + 10) - ais 10. Consider what that means forb - a(which is technically undefined behaviour, by the way).– rici
Nov 21 '18 at 6:03
@rici: I thought that would be
-(result)...– BinaryTreeee
Nov 21 '18 at 6:11