为什么这个计算字符串长度的 C 程序会给出错误的输出？

Question

我写了这个程序，它接受 string 作为输入和 return 它的长度。

#include<stdio.h>
#include<string.h>
#define MAX 100

int main()
{
    char a[MAX];
    int len;
    printf("Enter a string: ");
    fgets(a, MAX, stdin);

    len = strlen(a);
    printf("Length of the string = %d", len);

    return 0;
}

既然函数 strlen() 不计算空字符，即 '[=14=]'，为什么我的输出总是比输入 string 的字符多 1？

例如-

Enter a string: Aryan
Length of the string = 6
Process returned 0 (0x0)   execution time: 4.372 s
Press any key to continue.

Answer 1

如果提供的数组中有 space，函数 fgets 可以将换行符 '\n' 添加到输入的字符串中。

来自C标准（7.21.7.2 fgets函数）

2 The fgets function reads at most one less than the number of characters specified by n from the stream pointed to by stream into the array pointed to by s. No additional characters are read after a new-line character (which is retained) or after end-of-file. A null character is written immediately after the last character read into the array

因此在 strlen

的调用中

len = strlen(a);

换行符也算在内

您需要将其删除，例如

a[ strcspn( a, "\n" ) ] = '[=11=]';

或

char *p = strchr( a, '\n' );
if ( p != NULL ) *p = '[=12=]';

Answer 2

fgets() 调用包括从输入流中读取的换行符。这很有用，因为它允许您检查该行是否已被完整读取。如果输入的最后一个字符没有换行符，则读取的行不完整。

int main()
{
    char a[MAX];
    size_t len;   // being precise with your types is a good habit
    printf("Enter a string: ");
    fgets(a, MAX, stdin);

    len = strlen(a);

    if ( a[len - 1] == '\n' )
    {
        // Usually you don't want the newline in there.
        a[--len] = '[=10=]';
        // --len above corrected the length.
        printf("Length of the string = %zu\n", len);
    }
    else
    {
        printf("Length of the string longer than %d\n", MAX - 1);
        // You can repeat fgets() until you get the whole line,
        // or keep reading (and throwing away) from input until
        // you get a newline. It really depends on how you want
        // to handle the error.
    }

    return 0;
}

为什么这个计算字符串长度的 C 程序会给出错误的输出？

Why does this C program to calculate string's length give a wrong output?

c

newline

fgets

string-length

strlen