C++ - 对 execvp 的函数调用返回无法访问 C++ Shell 程序中的错误

Question

I am writing a simple shell program in C++. When I pass my arguments into execvp, in particular, for the ls command, I receive a ls: cannot access H p : Protocol error . A similar error occurs for other commands as well.

My strategy is the parse the input into a vector<vector<char> and then convert it into a char ** .

Here is the conversion code below:

//input is parsed from command-line above
vector< vector<char> > args_vector;

string s;
stringstream ss(input);

while(getline(ss, s, ' ')){
    vector<char> cv(s.begin(), s.end());
    cv.push_back('\0');
    args_vector.push_back(cv);
}

char *args[args_vector.size() + 1];

for(int i = 0; i < args_vector.size(); i++){
    char *arg = &args_vector[i][0];   
    args[i] = arg;
}

args[args_vector.size() + 1] = NULL;

Then I pass args into execvp in the following code below:

pid_t child_pid
int status;
child_pid = fork();

if (child_pid == 0) {
    execvp(args[0], args);
    cout << "Error: execution of command failed";
}
else {
    pid_t pid;
    do {
        pid = wait(&status);
    } while (pid != child_pid);
}

I am compiling the code with clang++ and on a Debian 8 VM on Mac OS X. Does anyone have idea whats going?

Answer 1

To elaborate on my guess for your problem: I guess that the tokenizing (the first snippet of code) is in a separate function, and it then returns which makes the vector of vectors of characters you have be destructed, so the pointers you save in the args array will no longer be valid. This leads to undefined behavior , and you are pretty lucky the program doesn't actually crash (which is a common symptom of undefined behavior).