Implicit declaration of function with structs-CodePudding

I am trying to fix my last implicit declaration of a function by creating the prototype function in my header file. The lab is to write structs and currently I have my Main.c, RandomNums.h, and RandomNums.c. My function in RandomNums.c is finished but I'm not sure how I should write it in RandomNums.h

Below is what I have for my RandomNums.c file and the issue is that SetRandomVals is an implicit declaration in Main.c

struct RandomNums SetRandomVals(int low,int high) {
    struct RandomNums r;
    r.var1= (rand() % (high -low   1))   low;
    r.var2= (rand() % (high -low   1))   low;
    r.var3= (rand() % (high -low   1))   low;
     
    return r;
}

Below is how I called SetRandomVals

RandomNums r = SetRandomVals(low, high);

The prototype I had tried was

SetRandomVals(int low,int high);

As for my professor, I may not edit the Main.c file.

EDIT: after adding the function prototype my new error is that I have an undefined reference after it had already stated I had an implicit declaration.

/tmp/ccOhjlhD.o: In function `main':
main.c:(.text 0x63): undefined reference to `SetRandomVals'
collect2: error: ld returned 1 exit status

CodePudding user response：

The prototype shall be the same as the function header in the definition: struct RandomNums setRandomVals(int low,int high).

and it should be declared before any caller calls the function.

CodePudding user response：

The return type needs to be included in the declaration.

And to do that, you will need to include the struct definition in the .h.

struct RandomNums { ... };

struct RandomNums setRandomVals(int low, int high);

By the way, you can avoid using the word struct everywhere by using a (possibly-anonymous) struct.

typedef struct { ... } RandomNums;

RandomNums setRandomVals(int low, int high);