c - 无法使用从 fgets 输入的字符串搜索字符

Question

我正在编写一个程序，使用 strchr 查找字符串中特定字符的位置。当使用 fgets 从用户输入字符串时，程序无法正常执行。

然而，当使用 gets 时一切正常。

使用 gets() 的代码:

#include <stdio.h>
#include <string.h>

int main() {
    char let;
    char input[50];
    char *ptr;
    printf("what is the string that you would like to check?\n");
    gets(input);
    printf("what is the character that you would like to find?\n");
    let = getchar();
    printf("in string \"%s\"...\n", input);
    ptr = strchr(input, let);
    while (ptr != NULL) {
        printf("the letter %c was found at character %d\n", let, ptr - input + 1);
        ptr = strchr(ptr + 1, let);
    }
    return 0;
}

输出:

what is the string that you would like to check?what is the character that you would like to find?in string "why is the world when wondering"...the letter w was found at character 1the letter w was found at character 12the letter w was found at character 18the letter w was found at character 23

Code that does not work usgin fgets():

#include <stdio.h>
#include <string.h>

int main() {
    char let;
    char input[50];
    char *ptr;
    printf("what is the string that you would like to check?\n");
    fgets(input, 16, stdin);
    printf("what is the character that you would like to find?\n");
    let = getchar();
    printf("in string \"%s\"...\n", input);
    ptr = strchr(input, let);
    while (ptr != NULL) {
        printf("the character is found at %d \n", ptr - input + 1);
        ptr = strchr(ptr + 1, let);
    }
    return 0;
}

输出:

what is the string that you would like to check?what is the character that you would like to find?in string "abcdefghijklmno"...

Answer 1

改变

fgets(input, 16, stdin)

到

fgets(input, sizeof(input), stdin)

当您将 16 的参数传递给 fgets() 时，您是在指示它读取不超过 15 个字符。为什么？

来自 fgets() 联机帮助页:

fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s.

如果您提供的多于 size -1 个字符，则剩余的字符留在输入缓冲区中。

然后当程序随后调用

let = getchar();

let 会被分配输入缓冲区中的下一个字符 - 甚至无需等待您输入任何其他内容。然后它会在您提供的字符串中搜索此字符 - 但在您提供的示例中找不到它。