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当strcpy在c中时,为什么编码会出错?

character-encoding file c

codez · 技术社区 · 8 年前

源代码:

char CUSTOMERS_FILE[50] = "customers.txt";

typedef struct Customer {
    char name[50];
    char password[50];
    char billing_address[100];
    char phone_number[15];
    double amount_paid;
    double amount_due;
    char date[20];
} Customer;

char* read_string(int length) {
    char data[length];
    rewind(stdin);
    fgets(data, length, stdin);

    if (data[0] == '\n') {
        data[0] = '\0';
    }

    strtok(data, "\n");

    printf("DATA: %s", data);

    return data;
}

void handle_modify_customer(Customer customer) {
    Customer edited_details;

    printf("\nMODIFYING DETAILS\n==============\n\n");

    printf("CREATE A CUSTOMER PROFILE\n=========================\n");

    printf("Name (%s): ", customer.name);
    strcpy(edited_details.name, read_string(50));

    printf("Password (%s): ", customer.password);
    strcpy(edited_details.password, read_string(50));

    printf("Billing Address (%s): ", customer.billing_address);
    strcpy(edited_details.billing_address, read_string(100));

    printf("Phone Number (%s): ", customer.phone_number);
    strcpy(edited_details.phone_number, read_string(15));

    printf("Amount Paid (%10.2lf): ", customer.amount_paid);
    scanf("%lf", &edited_details.amount_paid);

    printf("Amount Due (%10.2lf): ", customer.amount_due);
    scanf("%lf", &edited_details.amount_due);

    printf("Payment Date (%s): ", customer.date);
    strcpy(edited_details.date, read_string(20));

    /*
    if (strlen(edited_details.name) == '\0' || strlen(edited_details.billing_address) == '\0' || strlen(edited_details.password) == '\0' || strlen(edited_details.phone_number) == '\0' || strlen(edited_details.date) == '\0') {
        printf("All fields must be filled in!");
        handle_modify_customer(customer);
    }*/

    if (edited_details.name[0] == '\0' || edited_details.billing_address[0] == '\0' || edited_details.password[0] == '\0' || edited_details.phone_number[0] == '\0' || edited_details.date[0] == '\0') {
        printf("All fields must be filled in!");
        handle_modify_customer(customer);
    }

    FILE *file = fopen(CUSTOMERS_FILE, "r");
    FILE *new_file = fopen("customers_new.txt", "ab+");

    Customer record;

    while (fscanf(file, "[%[^]]], [%[^]]], [%[^]]], [%[^]]], [%lf], [%lf], [%[^]]]\n",
                  record.name, record.password, record.billing_address, record.phone_number,
                  &record.amount_paid, &record.amount_due, record.date) == 7)
    {
        if (strcmp(customer.name, record.name) == 0) {
            printf("P: %s\nD: %s", edited_details.phone_number, edited_details.date);
            fprintf(new_file, "[%s], [%s], [%s], [%s], [%lf], [%lf], [%s]\n", edited_details.name, edited_details.password, edited_details.billing_address, edited_details.phone_number, edited_details.amount_paid, edited_details.amount_due, edited_details.date);
        } else {
            fprintf(new_file, "[%s], [%s], [%s], [%s], [%lf], [%lf], [%s]\n", record.name, record.password, record.billing_address, record.phone_number, record.amount_paid, record.amount_due, record.date);
        }
    }

    fclose(file);
    fclose(new_file);

    remove(CUSTOMERS_FILE);
    rename("customers_new.txt", CUSTOMERS_FILE);

    printf("\nThe customer details have been successfully modified!\n");
    key_to_continue();
}

执行示例:

MODIFYING DETAILS
==============

CREATE A CUSTOMER PROFILE
=========================
Name (dumbfk): test
DATA: testPassword (abc123): lol
DATA: lolBilling Address (pukima jalan): lol
DATA: lolPhone Number (6969696969): 499449
DATA: 499449Amount Paid (   6969.00): 499449
Amount Due (6969699.00): 499494
Payment Date (6/9/1969): 22/2/2000
DATA: 22/2/2000P: ï¿½Oï¿½ï¿½ï¿½
D: ï¿½Oï¿½ï¿½ï¿½
The customer details have been successfully modified!

数据文件(之前):

[well lol], [abc123], [wtf bro? 24], [0183188383], [3000.000000], [4000.000000], [12/12/2012]
[chow hai], [abc123], [lol jalan], [6969696969], [6969.000000], [6969699.000000], [6/9/1969]
[lol head], [abc123], [lol jalan], [6969696969], [6969.000000], [6969699.000000], [6/9/1969]
[stupid face], [abc123], [lol jalan], [6969696969], [6969.000000], [6969699.000000], [6/9/1969]
[dumbfk], [abc123], [pukima jalan], [6969696969], [6969.000000], [6969699.000000], [6/9/1969]

数据文件(之后):

[well lol], [abc123], [wtf bro? 24], [0183188383], [3000.000000], [4000.000000], [12/12/2012]
[chow hai], [abc123], [lol jalan], [6969696969], [6969.000000], [6969699.000000], [6/9/1969]
[lol head], [abc123], [lol jalan], [6969696969], [6969.000000], [6969699.000000], [6/9/1969]
[stupid face], [abc123], [lol jalan], [6969696969], [6969.000000], [6969699.000000], [6/9/1969]
[test], [lol], [lol], [ï¿½Oï¿½ï¿½ï¿½], [499449.000000], [499494.000000], [ï¿½Oï¿½ï¿½ï¿½]

问题:

如您所见,问题是付款日期和电话号码字段变得混乱。就在我使用之后 strcpy . 我调试了 read_string(..) 功能很好。我不明白为什么会这样。如能帮助解决这个问题,我们将不胜感激。

有趣的是:只有 date 和 phone_number 受到影响。 name , password , billing_address 没有问题。

4 回复 | 直到 8 年前

klutt 8 年前

这是一个很好的例子,说明指针和数组是不同的:

char* read_string(int length) {
    char data[length];
    // code
    return data;
}

不会起作用,因为 data 是在堆栈上分配的本地数组,并且在函数返回时将不存在。

如果你改变 char data[length] 到 static char data[length] 它会起作用的但是,请注意,前面的读取将被覆盖,因此无法按预期工作:

char *s1, *s2;
s1 = read_string(10);
s2 = read_string(10);
printf("First string: %s\n", s1);
printf("Second string: %s\n", s2);

一个绕过它的方法就是 char data* = malloc(length * sizeof *data) . 这样你就可以使用以前的阅读。但总的来说你要避免隐藏 malloc 就像这样,因为你需要 free 他们之后如果您想采用这种解决方案,请执行以下操作:

char * read_string(char * dest, int length) {
    char data[length];
    // code
    return strncpy(dest, data, length);
}

然后这样称呼:

char * str = malloc(length);
if(! read_string(str, length)) {
    fprintf(stderr, "Error reading string\n");
    exit(EXIT_FAILURE);
}
// Code
free(str);

pm101 8 年前

将read_string函数中的本地字符数据更改为静态变量,这样内存就不会丢失

  #define MAX_STR_LENGTH 100

 char* read_string(int length) 
 {
    static char data[MAX_STR_LENGTH]; // change to static -- it will not change
    rewind(stdin);
    fgets(data, length, stdin);

    if (data[0] == '\n') {
        data[0] = '\0';
    }

    strtok(data, "\n");

    printf("DATA: %s", data);

    return data;
}

user3121023 8 年前

另一个选项是将指针与长度一起传递。

void read_string(char *data, int length) {

    fgets(data, length, stdin);

    if (data[0] == '\n') {
        data[0] = '\0';
    }

    strtok(data, "\n");

    printf("DATA: %s", data);

}

打电话

 read_string(edited_details.name, 50);

那就不用用了 strcpy()

-1

Igor S.K. 8 年前

在C语言中没有对字符串的直接支持。大多数时候你必须处理(我应该说“内存块”而不是“数组”?)包含字符和终止符的内存块 NUL 最后。

你的情况是这样的:

将字符串(一定数量的字符)从文件读入一大块记忆
你希望那块内存一直有效到你利用绳子
你用你的绳子。就这样。

第二个是你的代码中的错误。

char* read_string(int length) {
    /* "data" is your chunk of memory. 
     * It is an array. 
     * This array is local to containing function.
     * This array is automatically allocated on the stack.
     * This array has its address in memory. Like &data[0].
     * The address may change from one invocation of the function to another.
     */
    char data[length];

    /* some code here... */

    return data; /* true, this returns the address &data[0] */
} 
/* The function is done. Local variables (array by the name of "data") are gone.
 * The memory on the stack that was once allocated for local variables is  
 * considered "free-to-use" by any other function you will invoke next. This memory
 * is not valid for use outside the function any more, but you may and you do
 * return a pointer to that memory, which is dangerous to use and harmful 
 */

基本上有三种方法可以解决这个问题:

你要么声明一个全局内存块,比如说一个全局数组:

char data[MAX_POSSIBLE_LENGTH];  /* Static storage. Global scope. */  
char* read_string() {
    /* some code here... */
    return data; 
}

... 或者将数组设为固定长度的静态数组:

char* read_string() {
    static char data[MAX_POSSIBLE_LENGTH];  /* Static storage. Function scope. */  
    /* some code here... */
    return data; 
}

... 或者从外部传入数组及其长度:

char* read_string(char *data, int length) {
    /* some code here... */
    return data; 
}

…或使用动态分配

char* read_string(int length) {
    /* some code here... */
    char *data;
    data = malloc(length); /* Dynamic storage. Must be freed somewhere./* 
                           /* This is not an "array", now this really is a "chunk of memory" :) */

    return data; 
} 

void handle_modify_customer(Customer customer)
{
    Customer edited_details;
    char * input_str_ptr;

    printf("\nMODIFYING DETAILS\n==============\n\n");

    printf("CREATE A CUSTOMER PROFILE\n=========================\n");

    printf("Name (%s): ", customer.name);
    strcpy(edited_details.name, input_str_ptr = read_string(50));
    free(input_str_ptr); /* Don't allow mem leakage */

    /* ... */
}