c - C 语言的文件处理计算

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我想计算体重指数并将其写入文件。我尝试在另一个函数中计算它，如您所见，但输出仅为 0。然后我尝试了不同的函数，如 int 计算返回w/h*h 但他们都没有给我正确的答案。我找不到其他方法。

#include <stdio.h>
struct person
{
    int personId;
    double height;
    double weight;
    double BMI;
}; 

void calculate (double h, double w)
{
    struct person p1;
    p1.BMI = w / h*h ;
}
void write () {
FILE *file;
struct person p1;
file = fopen("bmi.txt","w");
if (file == NULL)
{
    printf("Error");
}
else
{
    printf("Person ID: "); scanf("%d",&p1.personId);
    printf("Height: "); scanf("%lf",&p1.height);
    printf("Weight: "); scanf("%lf",&p1.weight);
    calculate(p1.height,p1.weight);
    fwrite(&p1,sizeof(p1),1,file);

 }
fclose(file);
}

void read() {
FILE *file;
struct person p1;
file = fopen("bmi.txt","r");
if (file == NULL)
{
    printf("Error");
}
else
{
    while (!feof(file))
    {
        fread(&p1,sizeof(p1),1,file);
        printf("Person ID: %d\n",p1.personId);
        printf("Height: %f\n",p1.height);
        printf("Weight: %f\n",p1.weight);
        printf ("BMI: %f\n",p1.BMI);
    }
}
fclose(file);
}

int main () {
write();
read();
}

Answer 1

#include <stdio.h>

struct person {
    int personId;
    double height;
    double weight;
    double BMI;
}; 

double calculate (double h, double w){//change to return result
    return w / (h*h);//Need parentheses
}

void write_person(void){
    FILE *file;
    struct person p1;

    if ((file = fopen("bmi.dat", "ab")) == NULL){
        perror("fopen in write_person");
    } else {
        printf("Person ID : "); scanf("%d", &p1.personId);
        printf("Height(m) : "); scanf("%lf",&p1.height);
        printf("Weight(kg): "); scanf("%lf",&p1.weight);
        p1.BMI = calculate(p1.height,p1.weight);
        fwrite(&p1, sizeof(p1), 1, file);
        fclose(file);//Should be into else-block
     }
}

void read_person(void){
    FILE *file;
    struct person p1;

    if ((fopen("bmi.dat","rb")) == NULL){
        perror("fopen in read_person");
    } else {
        while (fread(&p1, sizeof(p1), 1, file) > 0){//don't use !feof(file) because EOF occurs at fread So Display of incorrect data.
            printf("Person ID: %d\n", p1.personId);
            printf("Height   : %.3f(m)\n", p1.height);
            printf("Weight   : %.1f(kg)\n", p1.weight);
            printf("BMI      : %.2f\n\n", p1.BMI);
        }
        fclose(file);
    }
}

int main (void) {
    write_person();
    read_person();

    return 0;
}