C中的冲突类型错误与某些文件io

Question

So here is my code

int main(int argc, char *argv[] )
{
    double mass1, mass2, tof, pixcm;
    char pofVfilename[50];
    double pix[50];
    double pofV[50];
    if(argc != 2)
    {
        printf("usage: %s filename", argv[0]); 
   }
else
    {
        FILE *file = fopen(argv[1], "r");
        if(file == 0){
            printf("could not open file\n");
        }
        else{
            fscanf(file, "%lf %lf", &mass1, &mass2);
            fscanf(file, "%lf", &tof);
            fscanf(file, "%s", pofVfilename);
            fscanf(file, "%lf", &pixcm);
            fclose(file);
            printf("%lf%lf%lf%lf", mass1, mass2, tof, pixcm);  
            readinputpofV(pix, pofV, pofVfilename);
            printf("%f %f", pix[10], pofV[10]);
        }

    }
    return 0;
}


void readinputpofV(double pix[], double pofV[], char filname[]){
    FILE *file = fopen(filname, "r");
    if(file == 0){
        printf("could not open pofV file\n");
    }
    else{
        int result = 2;
        int i = 0;
        while(result == 2){
            result = fscanf(file, "%lf %lf", &pix[i], &pofV[i]);
            i++;
        }
    }
    fclose(file);
}

The error I get is

warning: conflicting types for 'readinputpofV'

warning: previous implicit declaration of 'readinputpofV' was here

Can someone help. Also, I am brand new to file input and was hoping for some guidance on how I am doing.

Answer 1

This has nothing to do with the File I/O.

Try putting void readinputpofV(double pix[], double pofV[], char filname[]); above main() .

The call to the function is being taken as it's declaration, and the return type is being assumed as int . Hence the confusion.

Answer 2

previous implicit declaration of 'readinputpofV' was here

An implicit declaration makes the return type assumed to be int (in C89/C90, implicit declarations have been removed in C99). So the assumed type and the type of the definition are not compatible.

Therefore the compiler warns about the conflicting types.

It is just a warning, and not an error, though, and since the implemented type has void return type, you're not going to use the return value, so the code has a nonzero probability of working. But you should of course declare the function with the correct type before you are using it.

Answer 3

You have to declare the readinputpofV() function before using it, else the compiler will assume it returns int , whereas it later encounters that it really returns void .

What you should do is adding

void readinputpofV(double pix[], double pofV[], char filname[]);

before the definition of main() .

Answer 4

Since the compiler couldn't readinputpofV while is compiling main function is assuming that this function is returning an int If you move the definition of the function before the main. The warning will disappear.

Answer 5

Besides declaring the function prototype above main, you can write the whole definition of readinputpofV above main. Thus, you will avoid the error without needing to declare the function prototype.

---

I often use that tactic when I find it visually helpful, but it has it's downside: When you use multiple functions that interact with each other, that tactic may lead to compiler errors if you don't place the functions in the correct order. C programs are compiled serially; invoked functions should be known.

So, in C, to avoid implicit declaration compiler errors, any invoked function's definition or it's prototype, should be placed above any functions that might invoke it. You can just write them from bottom to top.