最短的C ++代码导致访问冲突

Question

Can we go shorter (character-wise) or more elegant than:

*(int*)0=0;

The goal is to raise an access violation. Platform independent solutions are preferred.

Answer 1

Assuming you are not including includes into your character count

For Linux:

raise(11); //SIGSEGV

For Windows:

raise(SIGSEGV); // I don't know the SIGSEGV value for sure so more characters required

Answer 2

There is no portable way of causing a segmentation violation or another similar error.

Compilers can and do assume that undefined behavior never occurs. If they detect UB in a certain branch of code, they have every right to optimize the entire branch out of existence.

if (x == 5) 
{
  std::cout << "Gonna crash";
  *(int*)0 = 42;
}

A compiler can translate this block of code to a no-op.

raise(SIGSEGV) may or may not cause an actual violation, but it is the only portable way of cause a program to behave as if a violation has occurred.

Answer 3

Here is the closest I could come using a different approach from the OP and MasterID:

asm("ret");

The idea is to manipulate the stack as clumsily as possible. I believe gcc will compile this.

Answer 4

From a Unix (mostly Linux) perspective:

If we define "access violation" as "any signal" that fills in the si_addr field of siginfo_t , then according to sigaction(2) that is: SIGILL, SIGFPE, SIGSEGV, SIGBUS, and SIGTRAP .

• SIGILL can be generated by executing any invalid instruction, including permanently invalid instructions such as ud2 on x86 (encoded as 0x0F 0x0B ), but jumping to a random point often generates this anyway.

• SIGFPE can be generated by dividing any integer by 0 or dividing the most negative integer by -1

• SIGSEGV can be generated by a read or write to any unmapped or PROT_NONE 'd page, or a write to a read-only page.

• SIGBUS I have never figured out where it comes from.

• SIGTRAP can be generated by your arch's breakpoint instruction, which on x86 is int3 , which is the single byte 0xcc . From one perspective, that is the shortest possible code. If you insist on the shorest possible C code you'd have to wrap it in an asm block according to your compiler's whims.

There are also other examples involving syscalls such as kill .