What is "Segmentation fault (core dumped)?" [duplicate]
I am trying to write a C program in linux that having sqrt of the argument, Here’s the code:
After I type in my input at the «shell> » prompt, gcc gives me the following error:
1 Answer 1
«Segmentation fault» means that you tried to access memory that you do not have access to.
The first problem is with your arguments of main . The main function should be int main(int argc, char *argv[]) , and you should check that argc is at least 2 before accessing argv[1] .
Also, since you’re passing in a float to printf (which, by the way, gets converted to a double when passing to printf ), you should use the %f format specifier. The %s format specifier is for strings ( ‘\0’ -terminated character arrays).
Segmentation fault (core dumped) — to where? what is it? and why?
When a segmentation fault occurs in Linux, the error message Segmentation fault (core dumped) will be printed to the terminal (if any), and the program will be terminated. As a C/C++ dev, this happens to me quite often, and I usually ignore it and move onto gdb , recreating my previous action in order to trigger the invalid memory reference again. Instead, I thought I might be able to perhaps use this «core» instead, as running gdb all the time is rather tedious, and I cannot always recreate the segmentation fault.
My questions are three:
- Where is this elusive «core» dumped?
- What does it contain?
- What can I do with it?
4 Answers 4
If other people clean up .
. you usually don’t find anything. But luckily Linux has a handler for this which you can specify at runtime. In /usr/src/linux/Documentation/sysctl/kernel.txt you will find:
core_pattern is used to specify a core dumpfile pattern name.
- If the first character of the pattern is a ‘|’, the kernel will treat the rest of the pattern as a command to run. The core dump will be written to the standard input of that program instead of to a file.
According to the source this is handled by the abrt program (that’s Automatic Bug Reporting Tool, not abort), but on my Arch Linux it is handled by systemd. You may want to write your own handler or use the current directory.
But what’s in there?
Now what it contains is system specific, but according to the all knowing encyclopedia:
[A core dump] consists of the recorded state of the working memory of a computer program at a specific time[. ]. In practice, other key pieces of program state are usually dumped at the same time, including the processor registers, which may include the program counter and stack pointer, memory management information, and other processor and operating system flags and information.
. so it basically contains everything that gdb needs (in addition to the executable that caused the fault) to analyze the fault.
Yeah, but I’d like me to be happy instead of gdb
You can both be happy since gdb will load any core dump as long as you have a exact copy of your executable: gdb path/to/binary my/core.dump . You should then be able to analyze the specific failure instead of trying and failing to reproduce bugs.
Also, if ulimit -c returns 0 , then no core dump file will be written.
You can also trigger a core dump manually with CTRL — \ which quits the process and causes a core dump.
The core file is normally called core and is located in the current working directory of the process. However, there is a long list of reasons why a core file would not be generated, and it may be located somewhere else entirely, under a different name. See the core.5 man page for details:
Segmentation Fault in C/C++
Segmentation faults in C or C++ is an error that occurs when a program attempts to access a memory location it does not have permission to access. Generally, this error occurs when memory access is violated and is a type of general protection fault. Segfaults are the abbreviation for segmentation faults.
The core dump refers to the recording of the state of the program, i.e. its resources in memory and processor. Trying to access non-existent memory or memory which is being used by other processes also causes the Segmentation Fault which leads to a core dump.
A program has access to specific regions of memory while it is running. First, the stack is used to hold the local variables for each function. Moreover, it might have memory allocated at runtime and saved on the heap (new in C++ and you may also hear it called the “free store“). The only memory that the program is permitted to access is it’s own (the memory previously mentioned). A segmentation fault will result from any access outside of that region.
Segmentation fault is a specific kind of error caused by accessing memory that “does not belong to you“:
- When a piece of code tries to do a read-and-write operation in a read-only location in memory or freed block of memory, it is known as a segmentation fault.
- It is an error indicating memory corruption.
Common Segmentation Fault Scenarios
In a Segmentation fault, a program tries to access memory that is not authorized to access, or that does not exist. Some common scenarios that can cause segmentation faults are:
- Modifying a string literal
- Accessing an address that is freed
- Accessing out-of-array index bounds
- Improper use of scanf()
- Stack Overflow
- Dereferencing uninitialized pointer
1. Modifying a String Literal
The string literals are stored in the read-only section of the memory. That is why the below program may crash (gives segmentation fault error) because the line *(str+1) = ‘n’ tries to write a read-only memory.
Segmentation fault (core dumped)
Segmentation fault (core dumped) в strcat
Сделал программу, в с новичок, но при вызове strcat выдоет ошибку: "Segmentation fault (core.
Segmentation fault (core dumped): ошибка при любом вводе после компиляции
Всем доброго времени суток. Не могли бы посмотреть программу и подсказать ошибку. При компиляции.
Сообщение от Nemovok
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Сообщение от Сергей2109
Сообщение от Сергей2109
Где информация о том, в каком именно месте кода это происходит? Почему она не приведена в вашем первом сообщении?
Существует миллион причин, по которым может произойти эта ошибка, и в вашем коде есть предпосылки для множества из этих причин. Каким образом вы предполагаете нам угадать, что вы передаете в эту функцию, существуют файлы, которые вы пытаетесь открывать, и что происходит в загадочной функции graph .
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Здравствуйте! Изучаю сейчас C. При компиляции в релизе возникает ошибка в такой, казалось бы.
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