在C99中，“函数”的类型冲突和函数“函数”的隐式声明无效

Question

The other answers on these questions say to declare the function either in a header file or before main() but I have both of these and it still doesn't work.

#include <stdbool.h>

#ifndef WORK
#define WORK

#define TRACING true
#define DIMENSION 4
#define TOUR_LENGTH 15

void trace(char *s); //error here "Conflicting types for 'trace'"

#endif

^that is the header file

void trace(char *s) //error here "Conflicting types for 'trace'"
{
    if (TRACING)
    {
        printf("%s\n",s);
    }
}

^the function in question. the function is used multiple times in other .c files all with #include work.h

#include <stdbool.h>
#include "work.h"
#include "gameTree.h"
#include "gameState.h"
#include "stack.h"
#include <stdio.h>


/*
    *   trace
    *   Provide trace output.
    *   Pre-condition: none
    *   Post-condition: if trace output is desired then the given String
    *                   parameter is shown on the console
    *   Informally: show the given message for tracing purposes
    *
    *   param s the String to be displayed as the trace message
*/
void trace(char *s) //error here "Conflicting types for 'trace'"
{
    if (TRACING)
    {
        printf("%s\n",s);
    }
}


/*
*   intro
*   Provide introductory output.
*   Pre-condition: none
*   Post-condition: an introduction to the progrm has been displayed
*   Informally: give the user some information about the program
*/
void intro()
{
    printf("Knight's Tour\n");
    printf("=============\n");
    printf("Welcome to the Knight's Tour.  This is played on a(n) %d x %d board.  The\n",DIMENSION,DIMENSION);
    printf("knight must move %d times without landing on the same square twice.\n",TOUR_LENGTH);
    printf("\n");
}


/*
*   main
*   Program entry point.
*   Pre-condition: none
*   Post-condition: the solution to the Knight's Tour will be found
*                   and displayed
*   Informally: solve the Knight's Tour
*/
int main(int argc, char *argv[])
    {
gameTree g,a;   // whole game tree and solution game tree
    gameState s;    // initial game state
    stack k,r;      // stack for intermediate DF use and for tracing solution
    queue q;        // queue for intermediate BF use

    // give introduction
    intro();

    // initialise data structures
    init_stack(&k);
    init_queue(&q);
    init_gameState(&s, 1, 1);   // start at top left-hand corner: (1,1)

    // show initial board
    printf("\nStarting board:\n");
    showGameState(s);
    printf("\n");

    // solve
    init_gameTree(&g, false, s, 1);
    a = buildGameDF(g, k, TOUR_LENGTH);     // Depth-first
    //a = buildGameBF(g, q, TOUR_LENGTH);   // Breadth-first

    // show results
    if (isEmptyGT(a))
    {
        printf("No solution!\n");
    }
    else
    {
        // re-trace solution from leaf to root
        init_stack(&r);
        do
        {
            push(r, a);
            a = getParent(a);
        } while (!isEmptyGT(a));

        // display move list
        while (!isEmptyS(r))
        {
            a = (gameTree)top(r);
            s = (gameState)getData(a);
            printf("Move %d: (%d,%d)\n", getLevel(a), getRow(s), getColumn(s));
            pop(r);
        }

        // display final path
        printf("\nFinal board:\n");
        showGameState(s);
    }

^the whole main() and .c file, the errors occur mainly in the other supplementary files with the ADT definitions such as:

gameTree getParent(gameTree t)
{
    gameTree p;

    trace("getParent: getParent starts"); //error here "Conflicting types for 'trace'" and "Implicit declaration of function 'trace' is invalid in C99"

    if (isEmptyGT(t))
    {
        fprintf(stderr, "getParent: empty game tree");
        exit(1);
    }

    init_gameTree(&p, true, NULL, -1);
    p->root = getTNParent(t->root);

    trace("getParent: getParent ends"); //error here "Conflicting types for 'trace'" and "Implicit declaration of function 'trace' is invalid in C99"
    return p;
}

^an example of where the trace function is called.

#include <stdbool.h>
#include "tNode.h"
#include "gameTree.h"
#include "work.h"
#include <stdlib.h>
#include <stdio.h>
#include <math.h>

^the imports for one of the ADT .c files

So yeah I don't know what to do.

To clarify work.h and work.c are the main files for this project.

void setChild(gameTree t, gameTree c)
{
    trace("setChild: setChild starts"); //error here "Implicit declaration of function 'trace' is invalid in C99"    
    setTNChild(t->root, c->root);

    trace("setChild: setChild ends"); //but not here
}


void setTNSibling(tNode t, tNode n)
{
    trace("setTNSibling: setTNSibling starts"); //both errors here

    t->sibling = n;

    trace("setTNSibling: setTNSibling ends"); //only the "Implicit declaration of function 'trace' is invalid in C99" error here
}

I can't determine what is causing certain errors but if it were to do with importing incorrect header files shouldn't it be consistent all the way through?

I should also note that these files were given to me to use so I didn't write the original trace function.

Answer 1

It is not clear from your code samples whether <ncurses.h> is included or not in some of your source files. There is a function trace already defined in <ncurses.h> on MacOS:

/usr/include/curses.h:1710:extern NCURSES_EXPORT(void) trace (const unsigned int);

If this is the actual problem, you need to rename your trace function to something else.

From the context, you should probably use a macro TRACE(...) that expands to a call to fprintf(stderr, __VA_ARGS__) unless you compile for the release build in which case it would expand to nothing at all.

Another potential cause for warnings is the prototype:

void trace(char *s);

Passing a string constant for a char * argument may cause a warning. Since trace does not modify the contents of the string argument, it should be declared const char * . Fix this by modifying the prototype:

void trace(const char *s);