expand array of struct using realloc C
I'm trying to expand the size of my array by 1 every time when I Enqueue
a new student , and it did work but the problem is it takes a garbage values for the name and id , can you please help me why is this happening ,
thanks .
void Enqueue(Student *arr , int index){
Student *s = NULL ;
int size = index + 1 ;
Student *temp = (Student*)realloc(s, size*(sizeof(Student)) );
if (temp == NULL){
printf("Can not allocate memory !!! n") ;
return ;
}
else
arr = temp ;
char Name[10] ; int Id ;
printf("please enter student name : n");
scanf("%s" , Name);
arr[size].name = Name ;
printf("please enter student ID : n");
scanf("%d" , &Id);
arr[size].id = Id ;
return ;
}
this is the run :
Student(5) Name :H�� H9�u�H�AA]A^A_Ðf. �
Student(5) ID : 1
c
asked Nov 15 '18 at 11:51
CsprogCsprog
13
add a comment |
I'm trying to expand the size of my array by 1 every time when I Enqueue
a new student , and it did work but the problem is it takes a garbage values for the name and id , can you please help me why is this happening ,
thanks .
void Enqueue(Student *arr , int index){
Student *s = NULL ;
int size = index + 1 ;
Student *temp = (Student*)realloc(s, size*(sizeof(Student)) );
if (temp == NULL){
printf("Can not allocate memory !!! n") ;
return ;
}
else
arr = temp ;
char Name[10] ; int Id ;
printf("please enter student name : n");
scanf("%s" , Name);
arr[size].name = Name ;
printf("please enter student ID : n");
scanf("%d" , &Id);
arr[size].id = Id ;
return ;
}
this is the run :
Student(5) Name :H�� H9�u�H�AA]A^A_Ðf. �
Student(5) ID : 1
c
asked Nov 15 '18 at 11:51
CsprogCsprog
13
Can we please have Student?
– Tsakiroglou Fotis
Nov 15 '18 at 11:54
2
Regardingarr[size].name = Name;- If this compiles, thenStudent::Namecan only be one of two things:void*orchar*(the latter far more likely). That means you're retaining a pointer to an automatic local variableNamein this function, which will produce undefined behavior the moment it is dereferenced outside this function. You need a real buffer (dynamic or fixed in theStudentstructure) andstrcpy(or scan directly into the target). And no, it's not the only bug.
– WhozCraig
Nov 15 '18 at 11:56
add a comment |
I'm trying to expand the size of my array by 1 every time when I Enqueue
a new student , and it did work but the problem is it takes a garbage values for the name and id , can you please help me why is this happening ,
thanks .
void Enqueue(Student *arr , int index){
Student *s = NULL ;
int size = index + 1 ;
Student *temp = (Student*)realloc(s, size*(sizeof(Student)) );
if (temp == NULL){
printf("Can not allocate memory !!! n") ;
return ;
}
else
arr = temp ;
char Name[10] ; int Id ;
printf("please enter student name : n");
scanf("%s" , Name);
arr[size].name = Name ;
printf("please enter student ID : n");
scanf("%d" , &Id);
arr[size].id = Id ;
return ;
}
this is the run :
Student(5) Name :H�� H9�u�H�AA]A^A_Ðf. �
Student(5) ID : 1
c
asked Nov 15 '18 at 11:51
CsprogCsprog
13
I'm trying to expand the size of my array by 1 every time when I Enqueue
a new student , and it did work but the problem is it takes a garbage values for the name and id , can you please help me why is this happening ,
thanks .
void Enqueue(Student *arr , int index){
Student *s = NULL ;
int size = index + 1 ;
Student *temp = (Student*)realloc(s, size*(sizeof(Student)) );
if (temp == NULL){
printf("Can not allocate memory !!! n") ;
return ;
}
else
arr = temp ;
char Name[10] ; int Id ;
printf("please enter student name : n");
scanf("%s" , Name);
arr[size].name = Name ;
printf("please enter student ID : n");
scanf("%d" , &Id);
arr[size].id = Id ;
return ;
}
this is the run :
Student(5) Name :H�� H9�u�H�AA]A^A_Ðf. �
Student(5) ID : 1
c
c
asked Nov 15 '18 at 11:51
CsprogCsprog
13
asked Nov 15 '18 at 11:51
CsprogCsprog
13
asked Nov 15 '18 at 11:51
CsprogCsprog
13
asked Nov 15 '18 at 11:51
CsprogCsprog
13
asked Nov 15 '18 at 11:51
CsprogCsprog
13
13
Can we please have Student?
– Tsakiroglou Fotis
Nov 15 '18 at 11:54
2
Regardingarr[size].name = Name;- If this compiles, thenStudent::Namecan only be one of two things:void*orchar*(the latter far more likely). That means you're retaining a pointer to an automatic local variableNamein this function, which will produce undefined behavior the moment it is dereferenced outside this function. You need a real buffer (dynamic or fixed in theStudentstructure) andstrcpy(or scan directly into the target). And no, it's not the only bug.
– WhozCraig
Nov 15 '18 at 11:56
add a comment |
Can we please have Student?
– Tsakiroglou Fotis
Nov 15 '18 at 11:54
2
Regardingarr[size].name = Name;- If this compiles, thenStudent::Namecan only be one of two things:void*orchar*(the latter far more likely). That means you're retaining a pointer to an automatic local variableNamein this function, which will produce undefined behavior the moment it is dereferenced outside this function. You need a real buffer (dynamic or fixed in theStudentstructure) andstrcpy(or scan directly into the target). And no, it's not the only bug.
– WhozCraig
Nov 15 '18 at 11:56
Can we please have Student?
– Tsakiroglou Fotis
Nov 15 '18 at 11:54
Can we please have Student?
– Tsakiroglou Fotis
Nov 15 '18 at 11:54
2
2
Regarding
arr[size].name = Name; - If this compiles, then Student::Name can only be one of two things: void* or char* (the latter far more likely). That means you're retaining a pointer to an automatic local variable Name in this function, which will produce undefined behavior the moment it is dereferenced outside this function. You need a real buffer (dynamic or fixed in the Student structure) and strcpy (or scan directly into the target). And no, it's not the only bug.– WhozCraig
Nov 15 '18 at 11:56
Regarding
arr[size].name = Name; - If this compiles, then Student::Name can only be one of two things: void* or char* (the latter far more likely). That means you're retaining a pointer to an automatic local variable Name in this function, which will produce undefined behavior the moment it is dereferenced outside this function. You need a real buffer (dynamic or fixed in the Student structure) and strcpy (or scan directly into the target). And no, it's not the only bug.– WhozCraig
Nov 15 '18 at 11:56
add a comment |
1 Answer
1
active
oldest
votes
realloc(s, size*(sizeof(Student)) ); must be realloc(arr, size*(sizeof(Student)) ); (s is NULL!).
Then, you never return the newly allocated array to the caller:
arr = temp does not change the passed in pointer. You'd need a pointer to a pointer to return the new value, like
void Enqueue(Student **arr , int index){
...
*arr = temp;
...
}
or just return the new array:
Student* Enqueue(Student *arr, int index) {
...
return temp;
}
And then there are the other memory management bugs, as mentioned by @WhozCraig.
answered Nov 15 '18 at 11:55
JimmyBJimmyB
9,53811838
add a comment |
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1 Answer
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oldest
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oldest
votes
realloc(s, size*(sizeof(Student)) ); must be realloc(arr, size*(sizeof(Student)) ); (s is NULL!).
Then, you never return the newly allocated array to the caller:
arr = temp does not change the passed in pointer. You'd need a pointer to a pointer to return the new value, like
void Enqueue(Student **arr , int index){
...
*arr = temp;
...
}
or just return the new array:
Student* Enqueue(Student *arr, int index) {
...
return temp;
}
And then there are the other memory management bugs, as mentioned by @WhozCraig.
answered Nov 15 '18 at 11:55
JimmyBJimmyB
9,53811838
add a comment |
realloc(s, size*(sizeof(Student)) ); must be realloc(arr, size*(sizeof(Student)) ); (s is NULL!).
Then, you never return the newly allocated array to the caller:
arr = temp does not change the passed in pointer. You'd need a pointer to a pointer to return the new value, like
void Enqueue(Student **arr , int index){
...
*arr = temp;
...
}
or just return the new array:
Student* Enqueue(Student *arr, int index) {
...
return temp;
}
And then there are the other memory management bugs, as mentioned by @WhozCraig.
answered Nov 15 '18 at 11:55
JimmyBJimmyB
9,53811838
add a comment |
realloc(s, size*(sizeof(Student)) ); must be realloc(arr, size*(sizeof(Student)) ); (s is NULL!).
Then, you never return the newly allocated array to the caller:
arr = temp does not change the passed in pointer. You'd need a pointer to a pointer to return the new value, like
void Enqueue(Student **arr , int index){
...
*arr = temp;
...
}
or just return the new array:
Student* Enqueue(Student *arr, int index) {
...
return temp;
}
And then there are the other memory management bugs, as mentioned by @WhozCraig.
answered Nov 15 '18 at 11:55
JimmyBJimmyB
9,53811838
realloc(s, size*(sizeof(Student)) ); must be realloc(arr, size*(sizeof(Student)) ); (s is NULL!).
Then, you never return the newly allocated array to the caller:
arr = temp does not change the passed in pointer. You'd need a pointer to a pointer to return the new value, like
void Enqueue(Student **arr , int index){
...
*arr = temp;
...
}
or just return the new array:
Student* Enqueue(Student *arr, int index) {
...
return temp;
}
And then there are the other memory management bugs, as mentioned by @WhozCraig.
answered Nov 15 '18 at 11:55
JimmyBJimmyB
9,53811838
edited Nov 15 '18 at 12:01
answered Nov 15 '18 at 11:55
JimmyBJimmyB
9,53811838
answered Nov 15 '18 at 11:55
JimmyBJimmyB
9,53811838
answered Nov 15 '18 at 11:55
JimmyBJimmyB
9,53811838
9,53811838
add a comment |
add a comment |
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Can we please have Student?
– Tsakiroglou Fotis
Nov 15 '18 at 11:54
2
Regarding
arr[size].name = Name;- If this compiles, thenStudent::Namecan only be one of two things:void*orchar*(the latter far more likely). That means you're retaining a pointer to an automatic local variableNamein this function, which will produce undefined behavior the moment it is dereferenced outside this function. You need a real buffer (dynamic or fixed in theStudentstructure) andstrcpy(or scan directly into the target). And no, it's not the only bug.– WhozCraig
Nov 15 '18 at 11:56