Segmentierungsfehler im c-Programm beim Sortieren von Strings

Question

Das Programm wird in die Blase geschrieben, um die vom Benutzer eingegebenen Daten im Format dd/mm/yyyy zu sortieren, wobei der Monat eine Zeichenfolge oder eine ganze Zahl sein kann. Nach der Kompilierung wird kein Fehler angezeigt, aber nach der Eingabe der Daten während der Ausführung tritt ein Fehler bei der Segmentierung auf. Ich kann den Fehler nicht erkennen. Außerdem bin ich relativ neu im Programmieren. Bitte helfen Sie.

#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

Die segfault ist auf nicht initialisierten Speicher. Wenn ich dieses Programm kompiliere, um nach Warnungen zu suchen, werden zwei Hauptkategorien von Problemen angezeigt: die nicht initialisierten Speicherzugriffe und die Zeichenfolgenvergleiche.

$ 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") { 
      ^~~~~~~~~~~ 

... ausgelassen wiederholt ...

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

Ändern Sie Code aus,

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); 
}} 

zu,

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); 
    }} 

Dies funktioniert ..