C Language, simple malloc question in functions

simple malloc question in functions

Author	Message
Gues #1 / 6	simple malloc question in functions hello, I have a question regarding malloc. I was under the assumption that variables declared in functions were local to that function and is freed when the function is exited. I was writing a program which declared a variable in a function and allocated space using malloc(). After about letting the program run for a few minutes, i discovered that the program started swapping to the hard drive for virtual memory (I use djgpp). The problem was fixed when I called free() before exiting the function. Does the memory still persist when allocated with malloc() (or similar dynamically allocating function) even when it exits the function? Thank you for any help.
Thu, 09 Sep 1999 03:00:00 GMT

Lawrence Kir #2 / 6	simple malloc question in functions Quote: >hello, >I have a question regarding malloc. I was under the assumption that >variables declared in functions were local to that function and is freed >when the function is exited. Automatic variables are created when the block they are defined in is entered and they are destroyed when that block is exited. For example: void foo(int x) /* Function parameters are created on entry to the function and destroyend when it exits / { static int t; / static variables always exist throughout the lifetime of the program / int y; / An automatic variable at the outermost block level in a function in effect is created when then function is entered and destroyed when the function returns / { int z; / An automatic variable in an inner block is created when the block is entered and destroyed when the block is left (execution falls out the bottom, the block is jumped out of, or a return is executed within the block. } Quote: } >I was writing a program which declared a >variable in a function and allocated space using malloc(). After about >letting the program run for a few minutes, i discovered that the program >started swapping to the hard drive for virtual memory (I use djgpp). The >problem was fixed when I called free() before exiting the function. Does >the memory still persist when allocated with malloc() (or similar >dynamically allocating function) even when it exits the function? Thank >you for any help. malloc'd memory persists until you free it. For example in: void bar(void) { void p =- malloc(100); return p; Quote: } p itself is a pointer variable, it is automatic and is destroyed when the function returns. However what it points to is an object allocated by malloc() and that is not automatic. It remains in existence until it is freed. The pointer value returned by bar() can be used by the caller to reference the malloc'd object. -- ----------------------------------------- -----------------------------------------
Thu, 09 Sep 1999 03:00:00 GMT

Szu-Wen Hua #3 / 6	simple malloc question in functions [...] : malloc'd memory persists until you free it. For example in: : void bar(void) : { : void p =- malloc(100); : return p; : } [...] This typo is corrected only because it's part of code. There shouldn't be a '-' after the '=' before malloc().
Thu, 09 Sep 1999 03:00:00 GMT

Al Bowe #4 / 6	simple malloc question in functions Quote: >I have a question regarding malloc. I was under the assumption that >variables declared in functions were local to that function and is freed >when the function is exited. I was writing a program which declared a >variable in a function and allocated space using malloc(). After about >letting the program run for a few minutes, i discovered that the program >started swapping to the hard drive for virtual memory (I use djgpp). The >problem was fixed when I called free() before exiting the function. Does >the memory still persist when allocated with malloc() (or similar >dynamically allocating function) even when it exits the function? Thank >you for any help. Dynamically allocated memory is not automatically freed when you exit the function unless the function is main() and your program exits. The memory will presist throughtout the program life unless you explicitly free it. It is good discipline, to free all allocated storage as soon as possible. Freed storage can be reallocated, making better use of a limited resource. Al Bowers Tampa, FL http://www.gate.net/~abowers/index.html
Thu, 09 Sep 1999 03:00:00 GMT

Jens Schweikhar #5 / 6	simple malloc question in functions # hello, # I have a question regarding malloc. I was under the assumption that # variables declared in functions were local to that function and is freed # when the function is exited. I was writing a program which declared a # variable in a function and allocated space using malloc(). After about # letting the program run for a few minutes, i discovered that the program # started swapping to the hard drive for virtual memory (I use djgpp). The # problem was fixed when I called free() before exiting the function. Does # the memory still persist when allocated with malloc() (or similar # dynamically allocating function) even when it exits the function? Thank # you for any help. Yes, it persists. Every object in C has a storage class. Automatic variable have storage class "automatic", which means their existence begins with the end of their declaration and ends on the closing brace of their respective compound statement. Objects in malloc()ed, calloc()ed or realloc()ed memory have storage class "allocated", which means their existence begins with a successful return from one of these functions and ends when free() or realloc() is called for the respective pointer (and of course, upon program termination.) The Standard is 20km away and I'm writing this from memory. More knowlegeable language lawyers please correct me. Jens -- Jens Schweikhardt http://www.uni-stuttgart.de/People/schweikhardt/home.html SIGSIG -- signature too long (core dumped)
Fri, 10 Sep 1999 03:00:00 GMT

Stephan Wilm #6 / 6	simple malloc question in functions Quote: > hello, > I have a question regarding malloc. I was under the assumption that > variables declared in functions were local to that function and is freed > when the function is exited. I was writing a program which declared a > variable in a function and allocated space using malloc(). This does NOT apply to "malloc()". You are responsible for releasing the memory allocated by "malloc()" yourself by calling "free()". Only the local variables disappear when leaving a function. Quote: > After about > letting the program run for a few minutes, i discovered that the program > started swapping to the hard drive for virtual memory (I use djgpp). The > problem was fixed when I called free() before exiting the function. Does > the memory still persist when allocated with malloc() (or similar > dynamically allocating function) even when it exits the function? See above: the memory alloocated by "malloc()" is not freed automatically at runtime, only at program termination is the total amount of allocated memory released and returned to the system. If you want to know more about dynamic memory, please read the "Section 7. Memory Allocation" in the c.l.c FAQ. You can get the FAQ at http://www.eskimo.com/~scs/C-faq/top.htm or at ftp://rtfm.mit.edu/pub/usenet/comp.lang.c/C-FAQ-list and it gets posted to this newsgroup regularly. Stephan
Sat, 11 Sep 1999 03:00:00 GMT

Page 1 of 1

[ 6 post ]