I have serious problem which is segmentation fault and i am %99.99 sure its because of rewind.
i have somewhat big loop and it runs about 1200 time. in each run of my loop i rewind(fp) in 2 different class method. in visual studio it goes up to 527 times and then when i look at the value of fp, it says unable to read memory. i copy the same code to matrix environment and it goes up to 1027 test.if i stop rewinding i dont get error but my result will be wrong.
now my question:
when each time i rewind, is anyway to delete it from memory at the end of my loop?
for example
FILE* fp;
fp=fopen("filename","r");
for(..;..;..)
{
rewind(fp);
//beginning of my code
.
.
.
//end of my code
is there any command i can use to clear fp from memory right here?
}
any comment makes me grateful
Related
Hi I am doing this simple program
#include <iostream>
#include <string>
using namespace std;
int main (){
string hi("Hi how are you");
for(int i = 0;i<4;i++)
cout<<hi<<endl;
return 0;
}
When I compiled it and run it, there were no issues, but when I try to debug it, every time the IDE program (Code::Block 16.01) steps in or out of string hi("hi how are you") it gives me a Segmentation Fault.
I know SF is when the program tries to access a space of memory that it is not supposed to access, and I know string class is a C-Sytle string that allocates memory dynamically, and deletes them automatically when the program is finished, hence there should be no issue in memory management, so this code shouldn't be a problem.
BUT in this code I don't understand why do I get a SF when I debug it. When I tried debugging it for the first time and stepped out of hi, there were no errors, but when I tried watching hi, it gave me a SF, and when I try to debug it again, and I steped into string hi I get S.F.
Screenshot of the error FYI
When I was search information about this issue I found entry in Code::Blocks forum, but it is quite old.
However, there is possibility of bug in GDB for MiniGW. If you want to be sure, you should look for this issue and its fix.
I know that this isn't full answer, but you should go to this posts and read they, there is some solution:
Code::Blocks forum's posts:
1. Watching std::string in debugger causes segfault?!?
2. Still having seg fault while watching a string....
I have the following code
fin.close();
open = inName + ".xxx";
fin.open(open.c_str(),ios::binary);
fin>>noskipws;
while (fin>>_4byte[0])
{
fout<<_4byte[0];
}
I also have fout open in binary mode too.
However, this code was working perfectly, but suddenly after adding a loop before it it stopped outputting all the data, it is missing somewhere around 33~55 bytes.
I tried removing every other fin.open and fin.close to keep this one, but I keep on getting the same issue which is the output file is missing some data.
_4byte is an unsigned char array.
So I solved it, the issue was that I only had to add fin.close() after the while loop. I'm not sure why it happened. Can someone explain the reason?
Edit:
Okay that was not the issue.
After this code I had a cin, it actually stops writing when it reaches the cin if it hadn't done writing yet.
In my C++ project, I encounter a very strange issue. It crashes with exit code 11 when I remove a certain log statement (cout).
This answer points to a source that explains exit code 11 (actually EAGAIN) with the following statement:
The system lacked the necessary resources to create another thread, or
the system-imposed limit on the total number of threads in a process
PTHREAD_THREADS_MAX would be exceeded.
But I am pretty sure don't create any additional threads in my code (at least not explicitly). So why does the error occur and why does it go away when I use the log statement?
For reference, I will post the code but it's of course completely out of context and basically the only relevant line is the one with the log statement.
PayloadRegionMapper(string mappingTechniqueName, string configPath = "")
: payload(PAYLOAD), config(Config(configPath)) {
cout << "construct PayloadRegionMapper" << endl; // if commented out, my program crashes....
frames = generateFrames();
setMappingTechnique(mappingTechniqueName);
}
Run the program using a debugger and then backtrace once the crash happens.
Using the bt and frame command you can get an idea about the behaviour of the program during the crashing situation.
gdb <executable>
.....<crash happened>
bt
<It will give you the stack frame >
frame <frame number>
Then look for the values and memory area there.
I have a program written in C++ that uses a lot the "system" function to run things like i would run in Shell (using Ubuntu 12.04 32 bits).
The things done in the "system" function generate several files that will be processed. In a second part of the program i process those files.
When the program ends, it doesn't delete those files that was generated by the "system" functions.
When i run the program for the first time it runs fine, when i run in a second time it gives me Segmentation fault (core dumped) in a given loop of the second part. It does less iterations each time i try to run. For example : First run = ran fine. Second run = Segmentation fault(core dumped) in iteration 200. Third run = Segmentation fault(core dumped) in iteration 199. And goes on...
I resolved the problem deleting all files it had generated by "system" function in the end of each "run" of the program.
My question is...any one has any clue about why was it happening?
EDIT*
Below is a few pseudocode to exemplify.....unfortunately i cant put the entire code, its like 600 lines.
int main(void){
// Part 1 of the program.....severam "system" producing files
system("bash produceSeveralFiles.sh");
// Part 2 of the program......process files produced in part 1
processFiles();
// My Solution that i dont know why solves it
system("rm AllFiles");
return 0;
}
EDIT*
Way i checked that it goes until the loop...
for(int i = 0; i < 300 ; i++){
printf("\n%d",i);
...//a few code here
printf("\n%d",i);
}
Second run i see "i" goes until 200....third run i see "i" goes until 199....and go on...thats the way i checked where it was giving the Segmentation Core (dumped).
EDIT*
O well im ashamed now, just checked the old Script that was generating the files before the program and it gives the same problem....if i do the generation in a separated file and then only runs the "processFiles()" in the program, it gives the same error. The old Script has an "rm files" command in the end that wasnt concerned about. (thx to user #beta....just checked the old script cause your commentary)
Well....but anyway the question continue, but now i know its not only with the "system" function.
My program only sometimes gets a Segmentation fault: 11 and I can't figure it out for the life of me. I don't know a whole lot in the realm of C++ and pointers, so what kinds of things should I be looking for?
I know it might have to do with some function pointers I'm using.
My question is what kinds of things produce Segmentation faults? I'm desperately lost on this and I have looked through all the code I thought could cause this.
The debugger I'm using is lldb and it shows the error being in this code segment:
void Player::update() {
// if there is a smooth animation waiting, do this one
if (queue_animation != NULL) {
// once current animation is done,
// switch it with the queue animation and make the queue NULL again
if (current_animation->Finished()) {
current_animation = queue_animation;
queue_animation = NULL;
}
}
current_animation->update(); // <-- debug says program halts on this line
game_object::update();
}
current_animation and queue_animation are both pointers of class Animation.
Also to note, within Animation::update() is a function pointer that gets passed to Animation in the constructor.
If you need to see all of the code, it's over here.
EDIT:
I changed the code to use a bool:
void Player::update() {
// if there is a smooth animation waiting, do this one
if (is_queue_animation) {
// once current animation is done,
// switch it with the queue animation and make the queue NULL again
if (current_animation->Finished()) {
current_animation = queue_animation;
is_queue_animation = false;
}
}
current_animation->update();
game_object::update();
}
It didn't help anything because I still sometimes get a Segmentation fault.
EDIT 2:
Modified code to this:
void Player::update() {
// if there is a smooth animation waiting, do this one
if (is_queue_animation) {
std::cout << "queue" << std::endl;
// once current animation is done,
// switch it with the queue animation and make the queue NULL again
if (current_animation->Finished()) {
if (queue_animation != NULL) // make sure this is never NULL
current_animation = queue_animation;
is_queue_animation = false;
}
}
current_animation->update();
game_object::update();
}
Just to see when this function would output without any user input. Every time I got a Segmentation fault this would output twice right before the fault. This is my debug output:
* thread #1: tid = 0x1421bd4, 0x0000000000000000, queue = 'com.apple.main-thread, stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
frame #0: 0x0000000000000000
error: memory read failed for 0x0
Some causes of segmentation fault:
You dereference a pointer that is uninitialized or that points to NULL
You dereference a deleted pointer
You write outside the bounds of the scope of allocated memory (e.g. after the last element of an array)
Run valgrind with your software (warning, it really slows things down). Its likely that memory has been overwritten in some way. Valgrind (and other tools) can help track down some of these kinds of issues, but not everything.
If its a large program, this could get very difficult as everything is suspect since anything can corrupt anything in memory. You might try to minimize the code paths run by limiting the program in some way and see if you can make the problem happen. This can help reduce the amount of suspect code.
If you have a previous version of the code that didn't have the problem, see if you can revert back to that and then look to see what changed. If you are using git, it has a way to bisect search into the revision where a failure first occurred.
Warning, this kind of thing is the bane of C/C++ developers, which is one of the reason that languages such as Java are "safer".
You might just start looking through the code and see if you can find things that look suspicious, including possible race conditions. Hopefully this won't take to much time. I don't want to freak you out, but these kinds of bugs can be some of the most difficult to track down.