緩沖區溢出或其他
[英]Buffer overflow or something else
問題描述
我正在創建一個有關座位預定的程序。 我被要求對某些變量使用unsigned short和unsigned int，因此這就是為什么要這樣設置它們的原因。 我有一個可以正常運行的程序。 但是，當我在函數內部傳輸所有內容時，一切似乎都可以正常工作，但是在我的結構內部， 奇怪的值開始被保存到整個位置 ..我只想保存文件的值（從第2行->結尾）文件）。 因為我有一個要初始化的結構，所以我必須先閱讀txt文件和數量的座位，因此我在函數（本地var）內部和主體中聲明了此變量（passenger）2次。問題？ 如果我不使用任何功能，一切正常！
所以有問題的代碼：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int i,j,numberofseats,temp;
char platenr[8],selection,buff[60];
char firstname[20];
char lastname[20];
char phone[11];
char *p;
typedef struct
{
char fullname[40];
unsigned short phonenr[10];
unsigned int seatnr;
}PASSENGERS;
void readfile( void)
{
FILE *businfo;
businfo = fopen ("bus.txt","r");
if (businfo == NULL)
{
printf("Error Opening File, check if file bus.txt is present");
exit(1);}
else
{
fscanf(businfo,"%s %d",platenr, &numberofseats);
printf("Bus Licence plate Nr is: %s and number of seats is: %d", platenr, numberofseats);
PASSENGERS passenger[numberofseats];
for (j=0;j<numberofseats;j++)
{passenger[j].seatnr=j+1;
strcpy(passenger[j].fullname,"\0");
}
while (fgets(buff,sizeof(buff),businfo)!=0)
{sscanf(buff, "%s %s %d %s", firstname, lastname, &temp,phone);
strcpy(passenger[temp-1].fullname,firstname);
strcat (passenger[temp-1].fullname, " ");
strcat(passenger[temp-1].fullname,lastname);
printf("%s",passenger[temp-1].fullname);
i=0;
for (p=phone;*p!='\0';p++)
{
(passenger[temp-1].phonenr[i])=*p -'0';
i++;
}
}
}
}
int main(void)
{
readfile();
PASSENGERS passenger[numberofseats];
3 個解決方案
解決方案1
1 2016-12-18 07:52:04
問題是您在函數readfile()中聲明了一個本地數組，並且一旦該函數終止，它就會丟失。 您需要能夠將更改返回給main() 。 為此，您有一些選擇。 一種是可以在main()聲明該數組，然后將函數更改為void readfile(PASSENGERS passenger[]) 。 在這種情況下，您將執行以下操作：
int main()
{
PASSENGERS passenger[numberofseats];
readfile(passenger);
// more code
基本上，您將傳遞一個指向存儲在數組中元素的內存位置的指針，該指針位於main()本地，該函數將填充數組，有效地返回更改。
另一種選擇是在函數中動態分配數組（帶有malloc()系列），並使其返回類似PASSENGERS *readfile(void)的指針。 如果在編譯時未知席位數，則此選項可能更合適，因此您需要在必要時動態增大或縮小數組。 但是，此選項將使您省去手動管理內存的負擔，例如在完成后free()分配已分配的內存。
因為您說您將從文件中讀取numberofseats ，所以后者是更好的主意，因此您的代碼將如下所示：
PASSENGERS *readfile(void)
{
FILE *businfo;
PASSENGERS *passenger;
businfo = fopen ("bus.txt","r");
// do the checks, read the numberofseats
passenger = malloc(numberofseats * sizeof *passenger);
// read the values, fill the array
fclose(businfo); // do not forget to close the file
return passenger;
}
int main()
{
PASSENGERS *passenger = readfile();
// more code
free(passenger);
return 0;
}
解決方案2
1 2016-12-18 07:53:23
函數foo名為x的變量與函數bar名為y的變量無關。 換句話說： passenger在main和passenger在readfile是不同的變量。 更改一個不會影響另一個。
您想要的可能更像這樣：
int main(void)
{
PASSENGERS passenger[numberofseats];
readfile(passenger);
^^^^^^^^^
Pass array as a pointer
....
}
和
void readfile(PASSENGERS* passenger)
{
....
// REMOVE THIS: PASSENGERS passenger[numberofseats];
}
在該通知旁邊：
// Global variables gets zero initialized
int i,j,numberofseats,temp;
^^^^^^^^^^^^
Becomes zero at start up
但您仍然可以在main中使用它：
PASSENGERS passenger[numberofseats];
那可能不是您真正想要的。
由於您嘗試讀取該函數中的座位數，因此它確實暗示您要使用動態內存分配。 喜歡：
PASSENGERS* readfile()
{
.....
.....
PASSENGERS* p = malloc(numberofseats * sizeof(PASSENGERS));
.....
.....
return p;
}
int main(void)
{
PASSENGERS* passenger = readfile();
.....
.....
free(passenger);
return 0;
}
如果您不希望動態分配 ，則必須將numberofseats的輸入移動到main ，這樣才能在聲明數組之前完成。
解決方案3
0 2016-12-18 12:05:57
好的，所以在開始動態分配之前，我要做的是在main開頭指定最大席位數，然后從此處完成我的代碼，如下所示。 我在第43、109行中有2條警告消息，似乎無法修復。
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int i,j,numberofseats,temp;
char platenr[8],selection;
char firstname[20],lastname[20];
char phone[11];
char *p;
typedef struct
{
char fullname[40];
unsigned short phonenr[10];
unsigned int seatnr;
}PASSENGERS;
void readfile(PASSENGERS passenger[])
{ char buff[60];
FILE *businfo;
businfo = fopen ("bus.txt","r");
if (businfo == NULL)
{
printf("Error Opening File, check if file bus.txt is present");
exit(1);}
else
{
fscanf(businfo,"%s %d",platenr, &numberofseats);
printf("Bus Licence plate Nr is: %s, and Number of Seats is: %d.", platenr, numberofseats);
for (j=0;j<numberofseats;j++)
{passenger[j].seatnr=j+1;
strcpy(passenger[j].fullname,"\0");
}
while (fgets(buff,sizeof(buff),businfo)!=0)
{sscanf(buff, "%s %s %d %s", firstname, lastname, &temp,phone);
strcpy(passenger[temp-1].fullname,firstname);
strcat (passenger[temp-1].fullname, " ");
strcat(passenger[temp-1].fullname,lastname);
i=0;
for (p=phone;*p!='\0';p++)
{
(passenger[temp-1].phonenr[i])=*p -'0';
i++;
}
}
}
}
void countfreeseats(PASSENGERS passenger[]){
int freeseats = 0;
for (j=0; j<numberofseats; j++)
{
strcmp(passenger[j].fullname,"\0")==0 ? freeseats = freeseats + 1 : freeseats ;}
printf ("There are %d Free Seats in this Bus. \n", freeseats);
printf("Seats that are Available are:\n");
for (j=0; j<numberofseats; j++)
{if (strcmp(passenger[j].fullname,"\0")==0)
printf ("%u\n", passenger[j].seatnr);
}
freeseats = 0;
}
void changeData(PASSENGERS *target){
unsigned short tempdigit;
printf("Enter Passenger's first name:");
scanf("%s",firstname);
printf("Enter Passenger's last name:");
scanf("%s",lastname);
strcpy(target->fullname,firstname);
strcat (target->fullname, " ");
strcat(target->fullname,lastname);
printf("Enter Passenger's phone Nr:");
scanf("%s",phone);
i=0;
for (p=phone;*p!='\0';p++)
{
(target->phonenr[i])=*p -'0';
i++;
}
}
void searchpassenger(PASSENGERS passenger[], char selection)
{ char tempsel,tmpfirst[20],tmplast[20];
unsigned short tempphone[10];
if (selection == '1')
{ printf("Enter Passenger's first name:");
scanf("%s",tmpfirst);
printf("Enter Passenger's last name:");
scanf("%s",tmplast);
strcat (tmpfirst, " ");
strcat(tmpfirst,tmplast);
for (j=0;j<numberofseats;j++)
if (strcmp(passenger[j].fullname,tmpfirst)==0)
printf ("Passenger %s has Seat Nr #: %u\n",tmpfirst,passenger[j].seatnr);
}
else if (selection == '2')
{ printf("Enter Passenger's Phone Nr:");
scanf("%s",phone);
i=0;
for (p=phone;*p!='\0';p++)
{
(tempphone[i])=*p -'0';
i++;
}
for (j=0;j<numberofseats;j++)
{if (strcmp(tempphone,passenger[j].phonenr)==0)
printf("Passenger %s has Seat Nr %hd already Booked",passenger[j].fullname,passenger[j].seatnr);
}
}
}
void cancelSeat(PASSENGERS *target){
strcpy(target->fullname,"\0");
for (i=0;i<10;i++)
target->phonenr[i]=0;
printf("Seat Nr %d is now Free",temp);
}
void showList(PASSENGERS passenger[])
{
printf("The following Seats are Booked: \n Name, PhoneNr, SeatNr\n\n"); /*Emfanisi minimatos*/
for (i=0; i<numberofseats; i++)
if (strcmp(passenger[i].fullname,"\0")!=0)
{
printf("%s, ",passenger[i].fullname);
for (j=0;j<10;j++)
{printf("%hu",passenger[i].phonenr[j]);}
printf(", %u\n",passenger[i].seatnr);
}
}
void writeFile(PASSENGERS passenger[])
{
FILE * output; /* Dilosi onomatos arxeiou */
output = fopen("output.txt","w"); /*dimiourgia i eggrafi pano se iparxon arxeio me onoma output.txt, mesw tis parametrou w*/
fprintf(output,"%s %d \n",platenr,numberofseats); /* mesw tis fprintf eksagogi pinakidas kai epikefalidas "Diagramma leoforeiou" sto arxeio output.txt. Allagi grammis opou xreiazetai*/
for (i=0; i<numberofseats; i++)
{if (strcmp(passenger[i].fullname,"\0")!=0)
{
fprintf(output,"%s ",passenger[i].fullname);
fprintf(output,"%u ",passenger[i].seatnr);
for (j=0;j<10;j++)
fprintf(output,"%hu",passenger[i].phonenr[j]);
fprintf(output,"%s","\n");
}
}
fclose(output); /* Kleisimo arxeiou*/
printf("File Saved as Output.txt");
}
int main(void)
{
PASSENGERS passenger[53];
readfile(passenger);
do{
printf("\n\nNeo Sistima Katagrafis Thesewn Leoforeiou\n");
printf("Please make a selection:\n\n");
printf("0. Exit\n");
printf("1. Empty Seats \n");
printf("2. Book Specific Seat \n");
printf("3. Advanced Search of Booked Seats\n");
printf("4. Cancel Seat Booking\n");
printf("5. Show List of Booked Seats\n");
scanf(" %c",&selection);
if (selection=='1')
countfreeseats(passenger);
else if (selection=='2')
{
printf("Please give seat nr (between 1 and %d) that you want to book:\n", numberofseats);
scanf("%d",&temp);
if (temp >numberofseats || temp <= 0)
{printf("Error: Seat nr should be between 1 and %d", numberofseats);}
else if (strcmp(passenger[temp-1].fullname,"\0")!=0)
printf("Error: Seat is already booked");
else
changeData(&passenger[temp-1]);
}
else if (selection=='3')
{
char tempsel;
printf("Do you want to search with Name (1) or Phone Nr (2)?\n");
scanf(" %c",&tempsel);
searchpassenger(passenger,tempsel);
}
else if (selection=='4')
{
printf("Please give Seat Nr (between 1 and %d) that you want to Cancel Booking:\n", numberofseats);
scanf("%d",&temp);
if (temp >numberofseats || temp <= 0)
{printf("Error: Seat nr should be between 1 and %d", numberofseats);}
else if (strcmp(passenger[temp-1].fullname,"\0")==0)
printf("Error: Seat is already free");
else
cancelSeat(&passenger[temp-1]);
}
else if (selection=='5') /*Menu 6 - Emfanisi listas kratimenon thesewn taksinomimenon kata ayksonta arithmo*/
{
showList(passenger);
}
} while (selection!='0');
{
writeFile(passenger);
}
}
緩沖區溢出
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