c - 如何在二进制 *.dat 文件中存储或打印信息？ C编程

Question

我想在二进制模式的 *.dat 文件中存储信息或从中读取信息。该文件包含以下数据(以二进制形式编码):

License: 123456
Owner: John Doe
Value: 10000.00

License: IAMDOE
Owner: Jane Doe
Value: 20000.00

这是我的代码:

#include <stdio.h>
#include <string.h>
#define MAXPLEN 80

typedef struct {    
    char none; /* used for registry initiated by '\0' ,should be ingnored */    
    char owner[MAXPLEN];
    char license[6];
    double value;
} veiculo_t;    


/* i need to use the following functions in the process */

void print_registry(veiculo_t *v)
{
    printf("Owner: %s - License: %.6s - Value: %.2lf \n", (*v).owner, (*v).license, (*v).value);
}

void read_registry(veiculo_t *v)
{
    char license2[8];
    printf("Name of the owner:\n");
    fgets((*v).owner,100,stdin);

    printf("License plate:\n");
    fgets(license2,10,stdin);
    memcpy(&(v->license),license2,6);

    printf("Value:\n");
    scanf("%lf",&(*v).value);
}

int op_menu() 
{
    int op;
    printf("\n0 - end\n");
    printf("1 - insert\n");
    printf("2 - print\n");
    printf("option: ");
    scanf("%d",&op);  
    getchar();        
    return op;
}

int main()
{
    int op;
    op_menu();

    if (op=1){
        /* !!!!!HELP HERE!!!!!! */
    }

    if (op=2){
        FILE *f=fopen("veic.dat", "rb");
        if (f == NULL) 
        {
            printf("Not opened!\n");
        }
        else
            /* !!!!!HELP HERE!!!!!! */
    }
}

不太了解“流”...一些提示将不胜感激!

Answer 1

首先，更改以下内容，否则您将永远无法进入“菜单”。

op = op_menu();    //op should be assigned by the return value of open_menu
if (op==1){...
if (op==2){...    // I believe you want '==' not '='

根据注释，您必须调用read_registry 方法。添加的代码:

    if (op==1){
        //insert
        veiculo_t *t = malloc(sizeof(veiculo_t));
        read_registry(t);
        FILE *f=fopen("veic.dat", "ab");
        if (f == NULL)
        {
            printf("open file failed\n");
        }
        fwrite(t, sizeof(char), sizeof(*t), f);
        free (t);
    }

    if (op==2){
        //print
        FILE *f=fopen("veic.dat", "rb");
        if (f == NULL)
        {
            printf("Not opened!\n");
        }
        else
        {
            veiculo_t *t = malloc(sizeof(veiculo_t));
            printf("sizeof t: %d\n", sizeof(*t));
            while(fread(t, sizeof(char), sizeof(*t), f))
                print_registry(t);
            free(t);
        }

示例代码仅供引用，我更想提供一种思考而不是答案，但似乎代码总是清晰而强大。在下面的例子中我写文件使用追加模式，如果你想每次都重新写文件，写文件时在fopen中改变模式。

希望对您有所帮助。