Segmentation Fault

An error in which a running Unix program attempts to access memory not allocated to it and terminates with a segmentation violation error and usually a core dump.

Segmentation Fault occurred when running c program that is reading or writing non-exist segment(physical memory space). Example, declare an array of int x[5] and you try putting or reading 6th item(s) that the cpu system to crash.

It can be a sporadic occurance; for example, in the program below, if you type 'Dragon' it works quite happily. It's overwriting some part of the memory with something it shouldn't be. But it doesn't segfault until you get to something like 'Dragon Dave is overwriting your memory!'. This is a buffer overrun, and that's *bad*, and a very, very large hole in your programs security.
#include  " stdio.h "
int  main()
{
/*  allocate 5 bytes for the string  */
   
char  name[ 5 ];
/*  enter a string - possibly much longer  */
   gets(name);
/*  display the string  */
   printf(
" Hello, %s. " ,name);
}

segmentation faults may also occur in case of hardware errors, f.e. hard-disk or Memory failure. to find out, try running memtest86 and/or any hard-disk diagnostic tools from the manufacturer

segmentation fault is a type of error which occurs when u try to access a non existant physical memory address. Sometimes during execution of a C program u freed  memory and then within the scope of the same program try again to use the same memory, then also the seg. fault occurs, this is due to the fact that untill the completion of the program the memory utilised is not returned to the operating system.

This is often caused by improper usage of pointers in the source code, dereferencing a null pointer, or (in C) inadvertently using a non-pointer variable as a pointer.


 
### Segmentation Fault 的原因分析 Segmentation fault 是一种运行时错误,通常由程序试图访问未分配给它的内存区域引起。这种错误可能源于多种情况,包括但不限于指针操作不当、数组越界以及非法内存访问等[^1]。 #### 常见的原因 1. **指针越界** 当尝试通过指针访问超出其合法范围的内存地址时,可能会触发 segmentation fault。例如,在 C 或 C++ 中,如果定义了一个指向字符串字面量的指针并修改该指针的内容,则会引发此错误[^2]。 ```c char *c = "hello world"; c[1] = 'H'; // 这里会引发 segmentation fault,因为字符串字面量存储在只读区 ``` 2. **空指针解引用** 如果程序中存在对空指针的操作(即 `NULL`),则可能导致 segmentation fault。这是因为任何针对 NULL 地址的有效操作都是非法的。 3. **野指针使用** 所谓“野指针”,是指那些已经释放但仍被使用的指针。当再次尝试访问这些已被销毁的对象时,就可能发生 segmentation fault[^2]。 4. **栈溢出** 函数调用层次过深或局部变量占用过多空间也可能导致 stack overflow 并最终表现为 segmentation fault[^1]。 5. **动态内存管理失误** 不恰当的 malloc/free 配合或者重复 free 同一块内存也会造成类似的崩溃现象。 --- ### 解决方法概述 为了有效定位和消除 segmentation fault 问题,可以采取如下措施: - **利用调试工具** 使用 GDB (GNU Debugger) 可帮助开发者追踪到发生异常的具体位置及其上下文环境信息。启动方式如下所示: ```bash gdb ./your_program_name run backtrace ``` - **增加诊断信息** 在可疑代码片段附近加入 printf() 输出语句或其他形式的日志记录机制以便于观察实际执行流程是否偏离预期路径[^1]。 - **静态代码检查** 工具如 cppcheck 对源文件进行扫描能够提前发现潜在隐患所在之处。 - **单元测试驱动开发** 编写详尽全面的功能验证脚本有助于尽早暴露隐藏缺陷从而减少后期维护成本投入比例上升风险[^1]。 --- ### 示例修正方案 对于前面提到的例子而言,只需稍作调整即可避免上述提及的风险因素之一——不可变字符串上的更改动作: ```c #include <stdio.h> #include <string.h> int main(){ char c[] = "hello world"; // 将原声明改为可写的字符数组形式 c[1] = 'H'; printf("%s\n", c); } ``` 这样就不会再遭遇同样的 runtime error 况状了! ---
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