cout 不向控制台打印任何内容

Question

I am trying to use cout to print out c strings from a dynamically allocated 2D char array called charArray . The snippet where I am printing is here:

for(int k=0; k<intSize; k++)
{
    std::cout<<"hello"<<std::endl;
    std::cout<<charArray[intSize-1-k]<<std::endl;
}


for(int i = 0; i<intSize; i++)
{
    delete [] charArray[i];
    std::cout<<i<<std::endl;
}
delete [] charArray;

intSize is how many C strings are in charArray . However, when I run the program, "hello" is printed once, and nothing else prints, not the charArray nor the i in the second for loop. I already confirmed earlier in my code that charArray is properly filled by successfully using cout . I ran gdb to try and find the issue, and in gdb the for loops are fully iterating through, so for some reason after the first cout , the couts stop working. I also tried to flush after every cout , but still the same thing.

Answer 1

Try this:

#include <iostream>
int main()
{
    const char*nul = nullptr;
    std::cout << "before "<< nul << "after\n";
 }

The output will be:

 before

This is what is happening to you - you are trying to print a nullptr string. One of charArray[intSize-1-k] is null. Possibly reading it out of bounds. Writing a null string sets badbit to std::cout .

To avoid this there are two things you can do:

1. Validate that a char* is not null, before printing it.

2. std::cout.exceptions(std::ostream::failbit); will make operator<< throw an exception at the offending line of code. A debugger can catch the exception, and let you find your bug easily (gdb has catch throw ). If you have an exception handler, don't forget to have it call std::cout.clear(); .