更改main的签名时为什么会出现段错误? [英] Why am I getting segfault when changing the signature of main?

问题描述

我正在尝试着进入C语言，并编写了此程序，该程序在随机位置显示kb的RAM.这是代码，它可以正常工作:

I am trying to get my feet into C, and wrote this program that displays a kb of my RAM in a random location. Here is the code, and it works fine:

#include <stdio.h>

int main(){
    char *mem;
    for(int i =0; i < 1024; i++){
        mem++;
        printf("%c", *mem);
    }
    return 0;
}

此后，我对代码进行了以下更改，每次运行程序时都会遇到段错误:

After that, I did the following change in my code, and I get segfaults every time I run my program:

#include <stdio.h>


// Just added this signature
int main(int argc, char *argv[]){
    char *mem;
    for(int i =0; i < 1024; i++){
        mem++;
        printf("%c", *mem);
    }
    return 0;
}

我的蜘蛛感觉告诉我，我得到的段错误是随机的，也应该在第一个示例中引起，但是一次又一次地运行不同的程序使它看起来像是可预测的行为.

My spider senses tell me that the segfaults I get are random, and should also be caused in the first example, but running the different programs again and again makes it look like predictable behaviour.

$ gcc -v
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk/usr/include/c++/4.2.1
Apple LLVM version 7.3.0 (clang-703.0.31)
Target: x86_64-apple-darwin15.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

推荐答案

您的摘录都调用未定义的行为尝试

1. 越界(mem++;，无分配)
2. 使用未初始化的值(访问*mem)

1. Go out of bound (mem++;, with no allocation)
2. use uninitialized values (accessing *mem )

当前版本.

请记住，指针不会神奇地继承(或获取)内存，通常，您需要使指针指向有效的对象.

Remember, pointers do not magically inherit (or acquire) memory, you need to make a pointer point to something valid, in general.

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