0

I face a strange issue while trying to get user input through my code. I am pretty sure that the issue is not with the code but related to OS like standard input stream (stdin) or something like that, but since I don't have another machine with similar OS setup (as it's practically impossible to find an SCO machine nowadays), I expect some programmatic workarounds to solve this. My program reads a stream of alphanumeric characters from the user terminated by a '\n'.

But no matter how I try this to achieve this by different means, it just accepts the initial 256 characters. Initially I suspected the issue is with the fgets function , but when I use try to read the same value from a file using fgets, its working as expected.

Approach 1: 

main()
{
  char szInLine[999]; 
  memset(szInLine, 0, sizeof(szInLine));

  fprintf(stdout, "\nPlease enter the encrypted value:\n");

  if (fgets(szInLine, 997, stdin) == NULL)
   return(1);

  fprintf(stdout, "Encrypted data string contains %i characters: %s\n", 
  strlen(szInLine), szInLine);
}

Approach 2:

while(ch = getc(stdin)) != EOF)
{

  if((*szInLine++ = ch) == '\n')
  {
    break; 
  } 
}
*szInLine = '\0';

fprintf(stdout, "Encrypted data string contains %i characters: %s\n", strlen(szInLine), szInLine);

Output for both cases : "Encrypted data string contains 256 characters: abcde.....

Other approaches I already tried but didn't succeed include changing the data type of the buffer which holds the value (from string to unsigned long), dynamically allocating memory to the buffer, setting stdin as unbuffered e.t.c.

OS environment : SCO Unix, 32bit Compiler: CC

4

2 回答 2

1

请参阅 SCO 网站上的 ioctl() 和 stty() 手册页。您应该能够通过测试终端与重定向来检索设置的差异。

于 2017-12-28T15:03:02.970 回答
0

好吧，您的程序（两者）都有错误：

/* you should include <stdio.h> so fgets() can return a char *,
 * If you don't, it's assumed fgets() returns an int value. */
#include <stdio.h>

main()
{
  char szInLine[999]; 
  memset(szInLine, 0, sizeof(szInLine)); /* you don't need this */

  fprintf(stdout, "\nPlease enter the encrypted value:\n");

  /* fgets accepts a buffer and its size, it will reserve space for
   * one '\0' char. */
  if (fgets(szInLine, sizeof szInLine, stdin) == NULL) {
   /* it is good to print some diagnostic if you receive EOF */
   return(1);
  }

  fprintf(stdout, "Encrypted data string contains %i characters: %s\n", 
  strlen(szInLine), szInLine);

  /* you should return 0, here */
  return(0);
}

第二个更糟糕：

/* unbalanced parenthesis, you lack a parenthesis after 'while' keyword */
while(ch = getc(stdin)) != EOF)
{

  if((*szInLine++ = ch) == '\n')
  {
    break; 
  } 
}
*szInLine = '\0';

/* if you move the pointer 'szInLine' it will always be pointing to the end of
 * the string, so this printf will show 0 characters and an empty string, you
 * had better to save the pointer at the beginning, so you don't lose the
 * reference to the string beginning.
 */
fprintf(stdout, "Encrypted data string contains %i characters: %s\n", strlen(szInLine), szInLine);

这应该有效：

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

int main()
{
    char buffer_in[1000];
    char buffer_out[1000];

    while (fgets(buffer_in, sizeof buffer, stdin)) {
         /* you'll get a line of up to 'sizeof buffer_in - 1' chars with an
          * ending '\n' (or a truncated if the line has more than 'sizeof
          * buffer_in - 1' chars. Also, you'll have a '\n' at the end of the
          * buffer, if the line filled partially the buffer. */
         fprintf(stderr, 
                "String read (%d chars): %s", /* this is why I don't put a '\n' here */
                strlen(buffer_in), 
                buffer_in);
         /* encrypt(buffer_in, sizeof buffer_in, buffer_out, sizeof buffer_out); */
    }
    /* here you got EOF */
    return 0;
}

或者如果你想使用getc()：

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

int main()
{
    /* it is very important that c be an int, see manual 
     * page of fgetc(), getch() or getchar() */
    int c;
    char buffer[1000], *p = buffer;

    /* we check for buffer length and for EOF.  As we are doing the hard
     * work ourselves, we have to check for 'sizeof buffer - 1' to allow
     * space for the '\0'. */
    while ((p < buffer + sizeof buffer - 1) && ((c = getchar()) != EOF)) {
        if (c == '\n') { /* A NEWLINE, act on buffer, and skip it. */
             *p = '\0'; /* end the string */
             printf("Read %d chars: %s\n", p - buffer, buffer);
             /* crypt it ... */
             /* ... */
             p = buffer; /* reset buffer */
             continue;
        }
        *p++ = c; /* add the character to the buffer */
    }
    /* here you got EOF */
    return 0;
}

最后一点：

不要发布代码片段，而是完整的示例，因为很难确定哪些错误是在此处复制代码时出错，或者哪些是您在原始程序中犯的错误。

于 2020-04-08T21:51:48.110 回答