strcats func crashing application

Question

I trying strcat_s function and crashing application. How to work this code?

char *test = "hello ";
strcat_s(test, strlen(test), "guys");
// like output "hello guys" but application crashing...

Answer 1

Since you're writing C++, you should be using std::string, not char*.

std::string test = "hello ";
test += "guys;

And if you need to pass that string to existing C++ code as a pointer, use the c_str() method:

extern void foo(const char*);
foo(test.c_str());

Answer 2

You're trying to modify a string literal. That is not allowed.

Your compiler should at least be warning you about that char* test, which should be const char* test to enforce immutability. In fact, since C++11, your code won't even compile!

Answer 3

In C++03

char *test = "hello ";

Is a deprecated conversion of a const char[N] to a char*. Trying to modify it with strcat is undefined behavior.

In C++11 and above You have ill formed code.

char *test = "hello ";

Is not legal C++. The type of "hello " is a const char[N]. That means when you call strcat you try to modify a constant string. If you turn up your warning level to compiler should tell you this.

You really should be using std::string and then you could have

std::string test = "hello ";
test += "guys;

And it will work just fine.

Answer 4

The pointer test points to read-only memory. Modifing the read-only memory causes app crash.

This will work:

char test[128];
strcpy(test, "hello ");
strcat_s(test, strlen(test), "guys");