用 fgets() 替换 gets()

Question

我一直在测试这个结构，我收到关于使用 gets 的警告。有人提到要改用 fgets 并将末尾替换为 '[=13=]'。有什么建议我可以更改我的代码来做到这一点吗？

void regCars(Car reg[], int *pNrOfCars) {
    char again[WORDLENGTH] = "yes", model[WORDLENGTH], tmp[WORDLENGTH];
    int year, milage;

    while (strcmp(again, "yes") == 0) {
        printf("Enter model:");
        gets(model);
        printf("Enter Year:");
        gets(tmp);
        year = atoi(tmp);
        printf("Enter milage:");
        gets(tmp);
        milage = atoi(tmp);
        reg[*pNrOfCars] = createCar(model, year, milage); 
        (*pNrOfCars)++;
        printf("Continue? (yes/no)");
        gets(again);
    }
}

Answer 1

举个例子

if (NULL != fgets(model, WORDLENGTH, stdin)) /* Read the string. */
{
  model[strcspn(model, "\r\n")] = '[=10=]'; /* Cut off \n and/or \r, if any. */
}

Answer 2

它比看起来要复杂一些。如果您随后处理超长输入的截断行并将其视为有效，则仅用 fgets() 替换 gets 没有多大意义。您只是用错误的行为替换了未定义的行为。

if( fgets(line, sizeof(line), fp) )
{
   if(!strchr(line, '\n'))
   {
      /* line is too long, what you do is up to you, but normally
         we will discard it */
      int ch;

      while( (ch = fgetc(fp)) != EOF)
        if(ch == '\n')
          break;

   }
   else
   {
       /* line is a normal line with a trailing '\n' (gets trims the '\n')           */
   }
}

Answer 3

您可以编写一个实用函数 mygets()，它接受 2 个参数：一个指向目标数组的指针及其大小：

char *mygets(char *dest, size_t size) {
    /* read a line from standard input and strip the linefeed if any */
    if (fgets(dest, size, stdin)) {
        dest[strcspn(dest, "\n")] = '[=10=]');
        return dest;
    }
    return NULL;
}

void regCars(Car reg[], int *pNrOfCars) {
    char model[WORDLENGTH], tmp[WORDLENGTH];
    int year, milage;

    for (;;) {
        printf("Enter model:");
        if (!mygets(model, sizeof mode))
            break;
        printf("Enter year:");
        if (!mygets(tmp, sizeof tmp))
            break;
        year = atoi(tmp);
        printf("Enter milage:");
        if (!mygets(tmp, sizeof tmp))
            break;
        milage = atoi(tmp);
        reg[*pNrOfCars] = createCar(model, year, milage); 
        (*pNrOfCars)++;
        printf("Continue? (yes/no)");
        if (!mygets(tmp, sizeof(tmp))
            break;
        if (strcmp(again, "yes") != 0)
            break;
    }
}

请注意，您可以使用 prompt() 输出问题并读取响应的函数分解更多代码：

char *prompt(const char *message, char *dest, size_t size) {
    printf("%s ", message);
    fflush(stdout);
    /* read a line from standard input and strip the linefeed if any */
    if (fgets(dest, size, stdin)) {
        dest[strcspn(dest, "\n")] = '[=11=]');
        return dest;
    }
    return NULL;
}

void regCars(Car reg[], int *pNrOfCars) {
    char model[WORDLENGTH], tmp[WORDLENGTH];
    int year, milage;

    for (;;) {
        if (!prompt("Enter model:", model, sizeof mode))
            break;
        if (!prompt("Enter year:", tmp, sizeof tmp))
            break;
        year = atoi(tmp);
        if (!prompt("Enter milage:", tmp, sizeof tmp))
            break;
        milage = atoi(tmp);
        reg[*pNrOfCars] = createCar(model, year, milage); 
        (*pNrOfCars)++;
        if (!prompt("Continue? (yes/no)", tmp, sizeof(tmp))
            break;
        if (strcmp(again, "yes") != 0)
            break;
    }
}

另请注意，此函数应采用 reg 数组的大小，以便在数组已满时停止提示更多输入。正如目前指定的那样，它具有与gets()相同的缺点，意外的输入将导致未定义的行为。

用 fgets() 替换 gets()

Replacing gets() with fgets()

c

gets

fgets