Scanf 需要的值比 C 语言中应该多的值

Question

我正在尝试学习结构，我正在使用此代码

#include <stdio.h>
struct elements
{
    char name[50];
    int semester;
    char  am[15];
}student[100];
void read_struct(struct elements p[]);
int i=0;
main()
{
    for (i=0;i<2;i++)
    {
        read_struct(student);
    }
    for (i=0;i<2;i++)
    {   printf("%dn",i);
        printf("%sn",student[i].name);
        printf("%sn",student[i].am);
        printf("%dn",student[i].semester);
    }
    system("pause");
}
void read_struct(struct elements p[])
{
    gets(student[i].name);
    gets(student[i].am);
    scanf("%dn",&student[i].semester);
}

我面临以下问题：在第二次迭代中，当我输入变量的值时，程序student[1].semester不会打印我输入的内容，而是等待我输入另一个数字，按 Enter 然后打印。每次获取和扫描后我都尝试了fflush(stdin)，但我遇到了同样的问题。

Answer 1

尝试替换

scanf("%dn", &student[i].semester);

跟

scanf("%d", &student[i].semester);

---

除此之外，fflush(stdin)调用未定义的行为，所以不要使用它。

Answer 2

你的代码在很多层面上都是错误的。我不会只是添加注释指出它们，而是向您展示一种"更正确"的方法：

#include <stdio.h>
#include <string.h>
struct elements
{
    char name[50];
    int semester;
    char  am[15];
};
#define MAX_STUDENTS 2
void read_struct(struct elements *p);
int main(void)
{
    struct elements students[MAX_STUDENTS];  /* No longer global */
    for (size_t i = 0;i < MAX_STUDENTS; ++i)
        read_struct(&students[i]);  /* Pass pointer to single structure */
    for (size_t i = 0;i < MAX_STUDENTS; ++i)
    {
        printf("%ldn", i);
        printf("%sn", students[i].name);
        printf("%sn", students[i].am);
        printf("%dn", students[i].semester);
    }
}
void read_struct(struct elements *p)
{
    /* fgets is safe, in that it will not overwrite your buffer */
    fgets(p->name, sizeof(p->name), stdin);
    fgets(p->am, sizeof(p->am), stdin);
    scanf("%d", &p->semester);
    /* Skip trailing whitespace (like the newline) in the input buffer
     * left after the `scanf` call above.
     * Do it by reading one character and see if it's a newline. If it's
     * not a newline, then read next character, and so on until we get
     * the newline. It's safe because we *know* there is a newline in the
     * input buffer after the `scanf` call above.
     */
    int c;
    while ((c = fgetc(stdin)) != EOF && c != 'n')
        ;
    /* The `fgets function leaves the newline in the buffer so we
     * have to remove it, if it's there.
     * This is done by first checking if the last character (strlen(...) - 1)
     * is a newline, and if it is then we change that newline to the string
     * terminator character so the string is terminated there.
     */
    if (p->name[strlen(p->name) - 1] == 'n')
        p->name[strlen(p->name) - 1] = '';
    if (p->am[strlen(p->am) - 1] == 'n')
        p->am[strlen(p->am) - 1] = '';
}

---

尾随空格不起作用的原因是，scanf函数将继续读取输入，直到看到非空格的内容。在这种情况下，在您输入最后一个数据后，scanf仍然想要读取并丢弃所有空格，它不知道用户不应该再输入任何输入。

您真的必须手动读取并跳过尾随空格，就像我在上面的程序中所做的那样。