C external errors and 1 warning

Question

I am getting these errors when trying to compile, and the only thing underlined is strcpy_s(name, strlen(input)+1, input); Which is the warning. This is part of an assignment and part of the instructions was to make both a Topic.c (the code below) and a Topic.h but no instructions on what to put in the .h file. I have never seen these errors before and have researched them but I cannot find references relevant to this issue. This is not a fix code assignment this should be ready to run I am only supposed to understand the concepts. Not sure what question to ask. I have checked several times to ensure the code was typed in correctly.

LNK2019 unresolved external symbol main referenced in function "int __cdecl invoke_main(void)" (?invoke_main@@YAHXZ)

and

LNK1120 1 unresolved externals

and 1 warning

C6387 'name' could be '0': this does not adhere to the specification for the function 'strcpy_s'.

   #include <stdio.h>
   #include <stdlib.h>
   #include <string.h>

   /*
   * Swap 1 method with scalars: why does this not work?
   */
   void swap1(int x, int y)
   {
       int temp = x;
       x = y;
       y = temp;
   }

   /*
   * swap 2 method with pointers: why does this work?
   */
   void swap2(int* x, int* y)
   {
       int temp = *x;
       *x = *y;
       *y = temp;
   }

   /*
   * Play Pointer method: Don't forget to clean up your malloc!
   */
   char* playPointer(char* input)
   {
       // Allocate memory to hold a copy of the input array, copy input to it, and 
          return a pointer to a new array
       // What is the advantage of assigning address of a variable to a pointer 
          variable?
       // Why does swap1() not work, and why does swap2() work?
       // How does strpy_s() make code more secure?
       // How does strpy_s() demonstrate defensive coding?
       // Look up strncpy() and compare it to strpy_s() How are they similar?

       char* name = malloc(strlen(input)+1);
       strcpy_s(name, strlen(input)+1, input);
       return name;
   }

You're missing the `main()` function. If this is not the main program, use the `-c` option when compiling to just create a `.o` file, not try to link it. — Barmar, Jan 21 '22 at 23:34
The warning is because you didn't check whether `malloc()` succeeded. — Barmar, Jan 21 '22 at 23:35
Why do you have `'''` before and after the code? If you're trying to mark a code block, it should be 3 backticks, not quotes, and they should be on the line BEFORE the code. But since you've indented the code, you don't need that marker. — Barmar, Jan 21 '22 at 23:36
Not sure how to check if malloc succeeded. Tried adding the main do I need int main()? Thanks for the tip on submitting code — user17997828, Jan 21 '22 at 23:49
I still get the same errors and also tried if (name != notNULL) just in case — user17997828, Jan 22 '22 at 00:05

score 0 · Answer 1 · answered Jan 21 '22 at 23:35

0

There is no main function in your code.

The main function in the C language is the program entry point and it has to be present to run the compiled program.

In your case the linker cant find it and reports the error.

answered Jan 21 '22 at 23:35

0___________

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I tried adding int main(void) outside of {} over the whole code but still get the same errors. – user17997828 Jan 21 '22 at 23:48

score 0 · Answer 2 · answered Jan 22 '22 at 00:10

0

If this is supposed to be a standalone program, rather than something linked into other programs, it needs a main() function.

To suppress the warning about name, wrap the code that calls strcpy_s() in an if statement that checks that malloc() succeeded.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*
 * Swap 1 method with scalars: why does this not work?
 */
void swap1(int x, int y)
{
    int temp = x;
    x = y;
    y = temp;
}

/*
 * swap 2 method with pointers: why does this work?
 */
void swap2(int* x, int* y)
{
    int temp = *x;
    *x = *y;
    *y = temp;
}

/*
 * Play Pointer method: Don't forget to clean up your malloc!
 */
char* playPointer(char* input)
{
    // Allocate memory to hold a copy of the input array, copy input to it, and return a pointer to a new array
    // What is the advantage of assigning address of a variable to a pointer variable?
    // Why does swap1() not work, and why does swap2() work?
    // How does strpy_s() make code more secure?
    // How does strpy_s() demonstrate defensive coding?
    // Look up strncpy() and compare it to strpy_s() How are they similar?

    char* name = malloc(strlen(input)+1);
    if (name != NULL) {
        strcpy_s(name, strlen(input)+1, input);
    }
    return name;
}

int main(void) {
    return 0;
}

answered Jan 22 '22 at 00:10

Barmar

741,623
53
500
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Ill try that thanks – user17997828 Jan 22 '22 at 00:20
This it generated an output with nothing but code 0 but the warning remains about name could be 0. C6387 'name' could be '0': this does not adhere to the specification for the function 'strcpy_s'. Should I add delete name; ? I read that somewhere, if so how do I define delete? – user17997828 Jan 22 '22 at 00:30
What output are you expected? The program doesn't do anything. – Barmar Jan 22 '22 at 00:31
lol code 0 should be good enough just was worried that the name warning is still there Thanks – user17997828 Jan 22 '22 at 00:33
See https://stackoverflow.com/questions/69146879/warning-c6387-visual-studio The compiler isn't smart enough to detect that the check prevents that problem. – Barmar Jan 22 '22 at 00:34
But https://stackoverflow.com/questions/66821678/c6387-for-memcpy-strcpy-and-strcpy-s says that adding the null check should work. Maybe it depends on the version of MSVC. – Barmar Jan 22 '22 at 00:36
Thanks again and I will check that link – user17997828 Jan 22 '22 at 00:37

C external errors and 1 warning

2 Answers2