Segmetation fault
| Wikipedia wrote: |
|---|
| generally an attempt to access memory that the CPU cannot physically address |
http://en.wikipedia.org/wiki/Segmentation_fault
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Maybe he thought segmentation faults weren't directly related to C++? I don't think they are either actually...
@ computerquip: That is correct, you can have a Segmetation Fault with any language that allows DMA.
One thing that I don't like about that Wikipedia article is that it doesn't mention that there are different types of SegFaults.
1.) A Local SegFault is when an application writes data to a part of itself that was not intended to hold a variable, or was intended for a different variable there by corrupting that instance of the application running in memory and causing at best undefined behavior. You should be able to cause this on purpose using a dynamically allocated array if you're curious to see what happens, but some compilers\IDE's might try to auto correct the issue.
2.) A Global SegFault is when an application tries to write to a memory address that doesn't exist inside the scope of the application. These are often caught by the Operating System and the offending process is terminated.
One thing that I don't like about that Wikipedia article is that it doesn't mention that there are different types of SegFaults.
1.) A Local SegFault is when an application writes data to a part of itself that was not intended to hold a variable, or was intended for a different variable there by corrupting that instance of the application running in memory and causing at best undefined behavior. You should be able to cause this on purpose using a dynamically allocated array if you're curious to see what happens, but some compilers\IDE's might try to auto correct the issue.
2.) A Global SegFault is when an application tries to write to a memory address that doesn't exist inside the scope of the application. These are often caught by the Operating System and the offending process is terminated.
A segmentation fault proper will only happen if the process tries to use (both read or write) memory that doesn't belong to it. That's why it's called a segmentation fault; it happens when the process violates segment/page boundaries. It can also happen if the process attempts an operation not allowed by the flags assigned to the page. E.g. attempting to write to read-only memory, or execute non-executable memory.
#1 is more properly a buffer overflow. It can lead to a segfault, depending on what is written and where, but the action by itself is not a segfault.
#1 is more properly a buffer overflow. It can lead to a segfault, depending on what is written and where, but the action by itself is not a segfault.
this error happened when I tried reading the value at address hold by a pointer when the pointer was set to NULL.
this shows that this happens when application try reading a illegal memory location
this shows that this happens when application try reading a illegal memory location
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