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pilar
Joined: 30 Jan 2008
Posts: 197
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| How to initialize or free a dynamic memory allocation |
 Posted: Mon Feb 12, 2024 11:01 am |
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Hi, Could someone tell me how to initialize or free a dynamic memory allocation in CCS, just for summary purposes I have the following code:
| Code: | #include <18F4620.h>
#fuses HS,WDT32768,PROTECT,NOLVP,MCLR,BROWNOUT,PUT
#use delay(clock=20MHz)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)// RS232 Estándar
#include <stdio.h>
char* myFuntion1() {
char message1[] = "Hello, from the function1";
return message1;
}
char* myFuntion2() {
char message2[] = "Hello, from the function2";
return message2;
}
void main() {
char* issue1;
char* issue2;
issue1 = myFuntion1();
issue2 = myFuntion2();
printf("%s\r\n", issue1);
printf("%s\r\n", issue2);
while (TRUE);
}
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Where when I call the two functions the results are passed to two pointers but when I try to print the contents It prints only the last one that has been called.
I need to initialize or free the pointer, can this be done?
The Functions 1 and 2 should not be modified |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19539
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| Posted: Mon Feb 12, 2024 12:10 pm |
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Your problem is not freeing a memory allocation, It is the dynamic nature
of temporary variables.
A variable declared inside a function _only exists while the function is
running, unless it is declared as static_. So neither 'message' variable
actually exists once you exit the function. The RAM they use is available
for re-use. Some of this is then used for the second variable. It is
fundamentally fallacious to pass a pointer to a temporary variable,
except to a function 'inside' another, where the variable will still exist
while you are still inside the outer function.
This is standard C.
If you want to pass a pointer to a variable to be used outside it either
needs to be global or static. |
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pilar
Joined: 30 Jan 2008
Posts: 197
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| Posted: Mon Feb 12, 2024 4:25 pm |
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| Telmah, thanks for the clarification, now I have it clearer. |
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leach67
Joined: 13 Feb 2024
Posts: 3
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| Posted: Fri Feb 16, 2024 5:41 am |
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| Ttelmah wrote: | Your problem is not freeing a memory allocation, It is the dynamic nature
of temporary variables.
A variable declared inside a function _only exists while the function is
running, unless it is declared as static_. So neither 'message' variable
actually exists once you exit the function. The RAM they use is available
for re-use. Some of this is then used for the second variable. It is
fundamentally fallacious to pass a pointer to a temporary variable,
except to a function 'inside' another, where the variable will still exist
while you are still inside the outer function.
This is standard C.
If you want to pass a pointer to a variable to be used outside it either
needs to be global or static. |
hey
thanks for this.. |
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