字符串转换的分段错误？

Question

我正在做一个加密项目，我正在做一个简单的测试，它从终端获取一个文件名并运行我的加密。我有以下加密代码，但出现以下分段错误：

terminate called after throwing an instance of 'std::logic_error'
  what():  basic_string::_M_construct null not valid<br><br>
Program received signal SIGABRT, Aborted.
0x00007ffff74ab428 in __GI_raise (sig=sig@entry=6)
    at ../sysdeps/unix/sysv/linux/raise.c:54
54  ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.

使用 gdb 运行跟踪后，我确认此故障是在以下 loc 之后触发的：

string plain(reinterpret_cast(fileContents), fileLength);

下面我的main函数调用了这段代码：

#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <string>
#include <fstream>
#include <limits>
#include <sstream>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "rc4_enc.c"
#include "rc4_skey.c"

using namespace std;
void foo(int);

int main(int argc, char * argv[]){
    if(argc!=2){
        cout << "Please enter the filename that you want to encrypt or decrypt\n";
        exit(2);
    }
    int fd;
    fd = open(argv[1], O_RDONLY);
    cout << "The file descriptor is " << fd << endl;
    //close(fd);// Can I modify it if it's closed?
    foo(fd);

    return 0;
}

功能如下：

void foo(int fd) {

     int fileLength = lseek(fd, 0, SEEK_END);
     unsigned char* fileContents;
     fileContents = (unsigned char*) calloc(fileLength, sizeof(char));
     pread(fd, fileContents, fileLength, 0);
     string plain(reinterpret_cast<char*>(fileContents), fileLength); // Segfault happens here. But why? 
        RC4_KEY key;
        int length = plain.size();
        unsigned char *buf = (unsigned char*)malloc(length+1);
        memset(buf, 0, length+1);

        ifstream pass;
        pass.open("pass.txt");
        if(!pass.good()){
            return;
        }
        else{
            string password;
            getline(pass,password);
            RC4_set_key(&key, password.length(), (const unsigned char*)password.c_str());
        }
        RC4(&key, length, (const unsigned char*)plain.c_str(), buf);
        string result((char*)buf, length);
        free(buf);
        const char *outputBuf = result.c_str();
        pwrite(fd, outputBuf, result.length(), 0);
        ftruncate(fd, result.length());
    }

Answer 1

我会将此作为评论，但没有足够的声誉。

文件有多大？ calloc 会失败并返回 NULL 吗？ 即使不是这样，检查 calloc 的返回值也可能是明智的。或者使用 new 操作符和 try/catch。