从stdin中读取fget时，为什么忽略第一个字符串? [英] Why is the first string ignored when reading with fgets from stdin?

问题描述

可能重复:
Dev-C ++输入已跳过

我正在尝试使用fgets从stdin中读取字符串数组，但是我要读取的第一个字符串始终被忽略.是什么导致此问题?

I am trying to read an array of character strings from stdin using fgets, but the first string I want to read is always ignored. What is causing this issue?

#include <stdio.h>

int main()
{
    int i;
    struct material
    {
        char name[30];
        float price, kg;
    };
    unsigned m,nr;
    printf("Lorry capacity=");
    scanf("%u", &m);
    printf("Number of materials=");
    putchar('\n');
    scanf("%u", &nr);
    struct material list[nr];
    for (i=0; i<nr; i++)
    {
        printf("Name=");
        fgets(list[i].name, 30, stdin);
    }
    putchar('\n');
    for (i=0; i<nr; i++)
    {
        printf("%s ", list[i].name);
    }
    return 0;
}

推荐答案

scanf("%u", &nr);
struct material list[nr];
for (i=0; i<nr; i++)
{
    printf("Name=");
    fgets(list[i].name, 30, stdin);

scanf(％u"，& nr); 将换行符保留在输入缓冲区中，因此 fgets 查找空行而无需进一步输入输入.

The scanf("%u", &nr); leaves the newline in the input buffer, so fgets finds an empty line without requiring further input to be entered.

出于这个原因(尤其是其中一个原因)，混合使用(f)scanf 和 fgets 通常是一个坏主意.

It is generally a bad idea to mix (f)scanf and fgets, for that reason (among others).

作为快速解决方案，请在第一个 fgets

As a quick fix, empty the input buffer before the first fgets,

int ch;
while((ch = getchar()) != EOF && ch != '\n');
if (ch == EOF) {
    // oops
}

更原则性的修复方法是，在使用 fgets 获得包括换行符的整行之前读取值，并使用 strtoul 或解码数字> sscanf .

A more principled fix would be to read in the values before using fgets to get an entire line including the newline, and decode the numbers with strtoul or maybe sscanf.

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