文字列のソート中にcプログラムでセグメンテーションエラーが発生する

Question

プログラムは、ユーザが入力した日付をdd/mm/yyyy形式でバブリングするように書かれています。月は文字列または整数です。コンパイル後にエラーは表示されませんが、実行中に日付を入力した後にセグメンテーションフォールトエラーが表示されます。私は間違いを理解することができません。また、私はプログラミングに比較的新しいです。助けてください。コード

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

void readElements(char **date, int n) { 
    printf("enter the dates in dd/mm/yyyy format where month can be a string or " 
      "an integer\n"); 
    for (int i = 0; i < n; i++) { 
     date[i] = (char *)malloc(50); 
     scanf("%s", date[i]); 
    } 
} 

char strcompare(char *a, char *b, int n, int length1, int length2) { 
    char *sub1, *sub2, *sub3, *sub4; 
    int c = 0, d = 0, e = 0, f = 0; 
    // comparing year 
    while (c < 4) { 
     sub1[c] = a[length1 - 4 + c]; 
     c++; 
    } 
    while (d < 4) { 
     sub2[d] = b[length2 - 4 + c]; 
     d++; 
    } 
    if (strcmp(sub1, sub2) > 0) { 
     return 'o'; 
    } else if (strcmp(sub1, sub2) < 0) { 
     return 'z'; 
    } else 
     // comparing month 
    { 
     for (int i = length1 - 6; i > 2; i--) { 
      sub3[e] = a[i]; 
      e++; 
     } 
     for (int i = length2 - 6; i > 2; i--) { 
      sub4[f] = b[i]; 
      f++; 
     } 
     if (strcmp(sub3, sub4) == 0) { 
      int g = 0, h = 0; 
      // comparing day 
      char *sub5, *sub6; 
      while (g < 2) { 
       sub5[g] = a[g]; 
       g++; 
      } 
      while (h < 2) { 
       sub6[h] = b[h]; 
       h++; 
      } 
      if (strcmp(sub5, sub6) > 0) { 
       return 'o'; 
      } else { 
       return 'z'; 
      } 
     } else { 
      if (sub3 == "january") { 
       strcpy(sub3, "01"); 
      } 
      if (sub4 == "january") { 
       strcpy(sub4, "01"); 
      } 
      if (sub3 == "february") { 
       strcpy(sub3, "02"); 
      } 
      if (sub4 == "february") { 
       strcpy(sub4, "02"); 
      } 
      if (sub3 == "march") { 
       strcpy(sub3, "03"); 
      } 
      if (sub4 == "march") { 
       strcpy(sub4, "03"); 
      } 
      if (sub3 == "april") { 
       strcpy(sub3, "04"); 
      } 
      if (sub4 == "april") { 
       strcpy(sub4, "04"); 
      } 
      if (sub3 == "may") { 
       strcpy(sub3, "05"); 
      } 
      if (sub4 == "may") { 
       strcpy(sub4, "05"); 
      } 
      if (sub3 == "june") { 
       strcpy(sub3, "06"); 
      } 
      if (sub4 == "june") { 
       strcpy(sub4, "06"); 
      } 
      if (sub3 == "july") { 
       strcpy(sub3, "07"); 
      } 
      if (sub4 == "july") { 
       strcpy(sub4, "07"); 
      } 
      if (sub3 == "august") { 
       strcpy(sub3, "08"); 
      } 
      if (sub4 == "august") { 
       strcpy(sub4, "08"); 
      } 
      if (sub3 == "september") { 
       strcpy(sub3, "09"); 
      } 
      if (sub4 == "september") { 
       strcpy(sub4, "09"); 
      } 
      if (sub3 == "october") { 
       strcpy(sub3, "10"); 
      } 
      if (sub4 == "october") { 
       strcpy(sub4, "10"); 
      } 
      if (sub3 == "november") { 
       strcpy(sub3, "11"); 
      } 
      if (sub4 == "november") { 
       strcpy(sub4, "11"); 
      } 
      if (sub3 == "december") { 
       strcpy(sub3, "12"); 
      } 
      if (sub4 == "december") { 
       strcpy(sub4, "12"); 
      } 
      if (strcmp(sub3, sub4) > 0) { 
       return 'o'; 
      } else { 
       return 'z'; 
      } 
     } 
    } 
} 

void Bubblesort(char **date, int n) { 
    int i, j; 
    char *t; 
    for (i = 0; i < n - 1; i++) { 
     for (j = 0; j < n - i - 1; j++) { 
      int length1 = strlen(date[j]); 
      int length2 = strlen(date[j + 1]); 
      if (strcompare(date[j], date[j + 1], n, length1, length2) == 'o') { 
       t = date[j]; 
       date[j] = date[j + 1]; 
       date[j + 1] = t; 
      } 
     } 
    } 
} 

void printarray(char **date, int n) { 
    printf("Sorted array:\n"); 
    for (int i = 0; i < n; i++) { 
     printf("%s\n", date[i]); 
    } 
} 

void main() { 
    int n; 
    char *date[50]; 
    printf("enter the number of elements that are to be sorted\n"); 
    scanf("%d", &n); 
    readElements(date, n); 
    Bubblesort(date, n); 
    printarray(date, n); 
} 

Answer 1

セグメンテーション違反が初期化されていないメモリを使用したためです。このプログラムをコンパイルして警告を探すと、初期化されていないメモリアクセスと文字列比較の2つの主要なカテゴリが示されます。

$ clang-3.8 -c -Wall -fPIE -fsanitize=memory sorting_.c -o sorting.o 
sorting_.c:59:16: warning: result of comparison against a string literal is unspecified (use strncmp instead) [-Wstring-compare] 
     if (sub3 == "january") { 
      ^~~~~~~~~~ 
sorting_.c:62:16: warning: result of comparison against a string literal is unspecified (use strncmp instead) [-Wstring-compare] 
     if (sub4 == "january") { 
      ^~~~~~~~~~ 
sorting_.c:65:16: warning: result of comparison against a string literal is unspecified (use strncmp instead) [-Wstring-compare] 
     if (sub3 == "february") { 
      ^~~~~~~~~~~ 

は...

sorting_.c:38:7: warning: variable 'sub4' is uninitialized when used here [-Wuninitialized] 
     sub4[f] = b[i]; 
     ^~~~ 
sorting_.c:15:34: note: initialize the variable 'sub4' to silence this warning 
    char *sub1, *sub2, *sub3, *sub4; 
           ^
            = NULL 
sorting_.c:34:7: warning: variable 'sub3' is uninitialized when used here [-Wuninitialized] 
     sub3[e] = a[i]; 
     ^~~~ 
sorting_.c:15:27: note: initialize the variable 'sub3' to silence this warning 
    char *sub1, *sub2, *sub3, *sub4; 
         ^
          = NULL 
sorting_.c:50:9: warning: variable 'sub6' is uninitialized when used here [-Wuninitialized] 
     sub6[h] = b[h]; 
     ^~~~ 
sorting_.c:44:24: note: initialize the variable 'sub6' to silence this warning 
     char *sub5, *sub6; 
        ^
         = NULL 
sorting_.c:46:9: warning: variable 'sub5' is uninitialized when used here [-Wuninitialized] 
     sub5[g] = a[g]; 
     ^~~~ 
sorting_.c:44:17: note: initialize the variable 'sub5' to silence this warning 
     char *sub5, *sub6; 
       ^
       = NULL 
sorting_.c:23:5: warning: variable 'sub2' is uninitialized when used here [-Wuninitialized] 
    sub2[d] = b[length2 - 4 + c]; 
    ^~~~ 
sorting_.c:15:20: note: initialize the variable 'sub2' to silence this warning 
    char *sub1, *sub2, *sub3, *sub4; 
       ^
        = NULL 
sorting_.c:19:5: warning: variable 'sub1' is uninitialized when used here [-Wuninitialized] 
    sub1[c] = a[length1 - 4 + c]; 
    ^~~~ 
sorting_.c:15:13: note: initialize the variable 'sub1' to silence this warning 
    char *sub1, *sub2, *sub3, *sub4; 
      ^
      = NULL 
sorting_.c:163:1: warning: return type of 'main' is not 'int' [-Wmain-return-type] 
void main() { 
^ 
sorting_.c:163:1: note: change return type to 'int' 
void main() { 
^~~~ 
int 

Answer 2

変更し、あなたに、

void readElements(char **date,int n) 
{printf("enter the dates in dd/mm/yyyy format where month can be a string or an integer\n"); 
for(int i=0;i<n;i++) 
{date[i]=(char*)malloc(50); 
scanf("%s",date[i]); 
printf("%d %s \n",i, str); 
}} 

に、

void readElements(char **date,int n) 
{printf("enter the dates in dd/mm/yyyy format where month can be a string or an integer\n"); 

for(int i=0;i<n;i++)  
{ 
     char *str ; 
     str = (char*)malloc(60); 

     date[i]= str; 

scanf("%s",str); 

printf("%d %s \n",i, str); 
    }} 

これは動作します。..