while循环Char阵列通过引用

Question

所以我试图确定一个学校任务的最长行。这是我认为有问题的代码。我不明白为什么“longest_line”在while循环中打印效果不错，但不会在循环外部打印。

int main() { 
    int ch; 
    char line[MAXLINE] = { '\n' };   /* current input line */ 
    char longest_line[MAXLINE] = { '\n' }; /* copy of longest line */ 

    while ((ch = readline(line, MAXLINE)) != EOF) { 
    if (longest(line, longest_line)) 
     copy(longest_line, line); 
    printf("Read Line: %s\n", line); 
    printf("Long Line: %s\n", longest_line); 
    } 

    printf("Print Long Line: %s\n", longest_line); 

这里是输出：

calc L 
copy 
Read Line: sdafasdfsadfsadfs 
Long Line: sdafasdfsadfsadfs 
calc L 
Read Line: sadfs 
Long Line: sdafasdfsadfsadfs 
calc L 
Read Line: sdfasdfsafd 
Long Line: sdafasdfsadfsadfs 
calc L 
Read Line: sadfsdf 
Long Line: sdafasdfsadfsadfs 
calc L 
Read Line: sadfs 
Long Line: sdafasdfsadfsadfs 
calc L 
Read Line: 
Long Line: sdafasdfsadfsadfs 
calc L 
Read Line: sfsafsdfsf 
Long Line: sdafasdfsadfsadfs 
Print Long Line: 

这就像longest_line获取循环，这没有任何意义我后删除。对不起，我是一个新手。感谢那个知道这个异常背后的技术原因的人。

这里是我的整个程序，如果你想运行它（我固定变量）

#include <stdlib.h> 
#include <stdio.h> 
#include <stdbool.h> 

#define MAXLINE 80 /* maximum input line size */ 

/* function declarations */ 
int readline(char line[], int max); 
void copy(char to[], char from[]); 
bool longest(char read_line[], char previous_line[]); 

/* print longest input line */ 

int main() { 
    int ch; 
    char line[MAXLINE] = { '\n' };   /* current input line */ 
    char longest_line[MAXLINE] = { '\n' }; /* copy of longest line */ 

    while ((ch = readline(line, MAXLINE)) != EOF) { 
    if (longest(line, longest_line)) 
     copy(longest_line, line); 
    printf("Read Line: %s\n", line); 
    printf("Long Line: %s\n", longest_line); 
    } 

    printf("Print Long Line: %s\n", longest_line); 

    return 0; 
} 

/* readline: read a line into s, return length */ 
int readline(char s[], int lim) { 
    int i = 0; // the current index 
    char c; // the current char 

    c = getchar(); 
    while (c != '\n' && i < lim) { 
    s[i] = c; 
    i++; 
    c = getchar(); 
    } 
    s[i] = '\0'; // final charachter of string 

    return c; 
} 

/* copy: copy 'from' into 'to'; assume to is big enough */ 
void copy(char to[], char from[]) { 
    int i; 
    for (i = 0; to[i] = from[i]; ++i); 
printf("copy\n"); 
} 

/* longest: Which line is the longest */ 
bool longest(char read_line[], char previous_line[]) { 
    printf("calc L\n"); 
    char ch; 
    int size_read = 0; 
    int size_previous = 0; 

    // determine length of read line 
    ch = read_line[size_read]; 
    while (ch != '\0') { 
    ch = read_line[size_read]; 
    ++size_read; 
    } 

    // determine length of previous line 
    ch = previous_line[size_previous]; 
    while (ch != '\0') { 
    ch = previous_line[size_previous]; 
    ++size_previous; 
    } 

    // determine longest line 
    if (size_read > size_previous) 
    return true; 
    else 
    return false; 
} 

Answer 1

我不会放弃的细节了，但也有在代码中的几个地方，你不能初始化变量，导致undefined behaviour。