C，将文件的指针作为参数传递给aa函数

Question

I am making a function to sort data in a txt file in order to produce the min, mean, and max of the data within.

I want to re-use the function on multiple files. Therefore, I'd like to pass the pointers for files into the function as an argument. However, my compiler gives me the following error:

LA1.c:19:10: error: unknown type name 'FILE' void mmm(FILE *ifile, int *i, int *min, int *max, float *mu);

I've attached my code below. Please exclude some of the extraneous variables as I anticipated using those later but have not finished the majority of this program. Any help is appreciated.

Thanks in advance.

/* Purpose: (1) Sort Data from 5 different years (2) Calculate Standard Deviation */
/* (3) find max & min from each set (4) calculate deviation standard deviation  */
/*  units, AKA σ (5) convert to letter grade */
/*************************************************************************/


/* Outline: (A) funct: scan data ifile (main) calc mean (μ), max, min  */
/* (B) funct: rescan data and calc sigma (C) main: Rescan data, calc Δ μετα' σ and letter */   
/* grade each for each datum.  (D) Print to minitor in main.  Use dow while?loop for rows*/
/*************************************************************************/

/*prototypes*/

void mmm(FILE *ifile, int *i, int *min, int *max, float *mu);   
/* mmm stands for min, max, mean */

float sigma (int *num, float *sigma);       /*calculates sigma(standard deviation) */

/* libraries */

#include <stdio.h>
#include <math.h>

void main (void) {

/* main variable declarations max of i vars used for rows loop counter in main */


float sigma, mu;
int i, i09, i10, i11, i12, i13, min, max, f09max, f09min, f10max, f10min, f11max, 
f11min, f12max, f12min, f13max, f13min;     

FILE *ifile;

ifile=fopen("2009.txt", "r");


mmm(&ifile, &i, &min, &max, &mu);

fclose(ifile);  /* file must be closed to rescan in other functions */

}

void mmm(FILE *ifile, int *i, int *min, int *max, float *mu) {

printf("running function mean \n");

int sum, num;

*max=0; /* Score range is between 0 and 100 in a class, thus use of fixed initials */
*min=100;
*i=0;
num=0;
sum=0;

    while (fscanf(ifile, "%i", &num) !=EOF)  {

    printf("Variable num is %i. \n", num);

    fscanf(ifile, "%d", &num);

        if (num>*max) {*max=num;} /* assigns global max and min */
        if (num<*min) {*min=num;} /* to be stored to different years in funct main*/

    *i=*i+1;

    sum= sum + num; /* sums for average calculation */

    }

*mu= ((float)sum/(*i));

printf("The min is %i.  The max is %i.\n", *min, *max);
printf("i is %i, sum is %i, and mu is %f \n", *i, sum, *mu);

}

Answer 1

You're declaring your function before the #include <stdio.h> line, so the compiler hasn't seen the definition of the FILE type yet. Just move your #include lines up to the top of the file.

Answer 2

In C the declarations of everything needs to be before they are used. Since you include the header file where FILE is declared after the function prototype where FILE is used, the compiler will not know what FILE is because by that point (at the function declaration) it haven't seen that declaration.

Answer 3

The '#include' statements in C are preprocessor directives. The preprocessor is a program invoked by the C compiler on your source code that follows the commands given in these directives and does text manipulation on the files before compilation. When it sees the `#include' statements, it grabs those files and inserts them into your code. By putting those directives after your function prototypes, you are making all types defined in those other source files only visible to the portion of your program following those directives. So, basically, put preprocessor directives like this at the very top of your program to make them usable by all of your code.