C ++调用getenv（“ LINES”）或getenv（“ COLUMNS”）在Xcode中运行良好，在终端中运行时出现段错误

Question

I'm trying to get the window size of my program when its run in terminal. In Xcode, I've edited the scheme so that the LINES and COLUMNS environmental variables are set for running within Xcode, and it runs fine there. But when I click the executable under Products and try running that within the Terminal, it segfaults. Any idea what I'm doing wrong? Does it have anything to do with my #includes ? Here's my basic code:

#include <iostream>

using namespace std ;

int main(int argc, const char * argv[]) {

    char* r = getenv("COLUMNS") ;

    cout << r << endl ;

    return 0;
}

Answer 1

If it segfaults in a terminal, it's almost certainly because the environment variable does not exists, hence r will be NULL . So your program would be better off checking for that:

#include <iostream>
#include <cstdlib>

int main (int argc, const char * argv[]) {
    char *r = std::getenv ("COLUMNS");
    std::cout << ((r == NULL) ? "?" : r) << '\n';
    return 0;
}

Run the following command from a terminal and see what you get:

echo "!$COLUMNS!"

If it's !! , you'll need to figure out how to get the variables set (and exported so that they appear to sub-processes), such as with:

COLUMNS=$(tput cols)
export COLUMNS