盡管其他所有內容都存盤了，但我的scanf輸入之一沒有被存盤

我對 C 語言作業非常陌生，所以如果我剛剛犯了一個簡單的錯誤，請原諒我，但我非常困惑。我的代碼如下：

#include <stdio.h>
#include <string.h>
int
main ()
{
  char first[10],last[10],address[20],city[10],state[3],zipcode[5];
  printf("\n\nPart 3:\n");
  printf("Please enter your name and address:\n");
  printf("First Name: ");
  scanf("%s", first);
  printf("Last Name: ");
  scanf("%s", last);
  printf("Address: ");
  fgetc(stdin);
  fgets(address, 20, stdin);
  address[strcspn(address,"[/r/n]")] = 0;
  printf("City: ");
  scanf("%s", city);
  printf("State: ");
  scanf("%s", state);
  printf("Zipcode: ");
  scanf("%s", zipcode);
  printf("%s %s\n%s%s, %s,  %s",first,last,address,city,state,zipcode);

  return 0;
}

一切正常，除非首先讀取最終的列印陳述句不輸出，它只是以姓氏開頭。例子：

對于輸入

Please enter your name and address:
First Name: Ben
Last Name: Johnson
Address: 1234 Smith St
City: Townsville
State: CA
Zipcode: 12345

我得到以下輸出：

 Johnson
1234 Smith St
Townsville, CA, 12345

只是不確定哪里出了問題，因為我的第一個變數的輸入方式與其他正在作業的變數完全相同。

uj5u.com熱心網友回復：

您正在寫入陣列city并且zipcode超出范圍，這會導致未定義的行為。

輸入字串Townsville是10字符長，因此它需要11包括終止空字符在內的字符。但是，該陣列city只有10字符空間，因此不足以存盤該字串。因此，當scanf嘗試存盤Townsville到中時city，它會溢位緩沖區。

陣列zipcode也有同樣的問題。對于所述輸入12345，它需要 6 個字符（包括終止空字符），但您只為5字符提供了陣列空間。

為了防止將來出現此類問題，我建議您使用fgets所有資料，因為fgets永遠不會溢位緩沖區，前提是您傳遞正確大小的緩沖區（您在發布的代碼中執行此操作）。但是，這將意味著大量額外的代碼，因為您還必須撰寫代碼以在每次呼叫時洗掉換行符fgets。因此，最好撰寫自己的函式。此函式還可以驗證是否已讀入整行，如果緩沖區不夠大，則列印錯誤訊息。

我已經重寫了您的代碼以使用這樣的功能：

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

void get_line_from_user( char *buffer, int buffer_size );

int main( void )
{
    char first[10],last[10],address[20],city[10],state[3],zipcode[5];

    printf("Part 3:\n");
    printf("Please enter your name and address:\n");

    printf("First Name: ");
    get_line_from_user( first, sizeof first );

    printf("Last Name: ");
    get_line_from_user( last, sizeof last );

    printf("Address: ");
    get_line_from_user( address, sizeof address );

    printf("City: ");
    get_line_from_user( city, sizeof city );

    printf("State: ");
    get_line_from_user( state, sizeof state );

    printf("Zipcode: ");
    get_line_from_user( zipcode, sizeof zipcode );

    printf("%s %s\n%s%s, %s,  %s",first,last,address,city,state,zipcode);

    return 0;
}

//This function will read exactly one line of input from the
//user. On failure, the function will never return, but will
//print an error message and call "exit" instead.
void get_line_from_user( char *buffer, int buffer_size )
{
    char *p;

    //attempt to read one line of input
    if ( fgets( buffer, buffer_size, stdin ) == NULL )
    {
        printf( "Error reading from input\n" );
        exit( EXIT_FAILURE );
    }

    //attempt to find newline character
    p = strchr( buffer, '\n' );

    //make sure that entire line was read in (i.e. that
    //the buffer was not too small to store the entire line)
    if ( p == NULL )
    {
        //a missing newline character is ok if the next
        //character is a newline character or if we have
        //reached end-of-file (for example if the input is
        //being piped from a file or if the user enters
        //end-of-file in the terminal itself)
        if ( getchar() != '\n' && !feof(stdin) )
        {
            printf( "Line input was too long!\n" );
            exit( EXIT_FAILURE );
        }
    }
    else
    {
        //remove newline character by overwriting it with
        //null character
        *p = '\0';
    }
}

現在，如果輸入太長，程式會給你一個正確的錯誤訊息，而不是溢位緩沖區：

Part 3:
Please enter your name and address:
First Name: Ben
Last Name: Johnson
Address: 1234 Smith St
City: Townsville
Line input was too long!

標籤：C 打印 扫描

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