Why is fscanf changing values of structure without explicitly being told to? - c

Question

I am trying to read a text file into a structure in c, but on the last iteration of my fscanf() loop, it changes both the numbers and text stored in the first and some of the second parts of my structure.
Debugging has revealed that this behaviour is caused by the while fscanf() loop. Although changing the size of the strings input prevented the numbers being changed, the string on the first line PMs.Party[0] still changed from = Labour to r. Here is my code:
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
void PartyPwr( int Runs, int Time[12], char Prty[12][15]);
struct Data
{
char *Name[12][15];
int StrtMnth[12];
int StrtYr[12];
int EndMnth[12];
int EndYr[12];
char Party[12][15]; // if this is 13 20 it runs without numbers changing.
int TimePwr[12];
};
int main(void)
{
int Max=0;
int i=0;
FILE *PriMins;
struct Data PMs;
if ((PriMins=fopen("PM.txt", "r")) == NULL)
{
printf("Error: PM.txt cannot be read.");
system("pause");
return(1);
}
while(fscanf(PriMins, "%s %d %d %d %d %s", &PMs.Name[Max], &PMs.StrtMnth[Max], &PMs.StrtYr[Max], &PMs.EndMnth[Max], &PMs.EndYr[Max], &PMs.Party[Max]) > 0)
{
PMs.TimePwr[Max]=((PMs.EndMnth[Max] +(PMs.EndYr[Max]*12)) - (PMs.StrtMnth[Max] + (PMs.StrtYr[Max]*12)));
printf("%s %d Total term %d\n",PMs.Name[Max], PMs.EndMnth[Max],PMs.TimePwr[Max]);
printf("Max val, %d bug check %d, %d, Party %s\n",Max, PMs.TimePwr[0], PMs.TimePwr[1], PMs.Party[0]);
Max++;
}
//PartyPwr(Max, PMs.TimePwr, PMs.Party);
//printf("%d, %d", PMs.TimePwr[0], PMs.TimePwr[1]);
fclose(PriMins);
system("pause");
return(0);
}
void PartyPwr( int Runs , int Time[12], char Prty[12][15])
int i=0;
int LabPwr=0;
int ConPwr=0;
for (i=0;i<Runs;i++)
{
printf("%s\n", Prty[i]);
if (strcmp(Prty[i],"Labour")==0)
{
LabPwr=(LabPwr+Time[i]);
}
if (strcmp(Prty[i],"Conservative")==0)
{
ConPwr=(ConPwr+Time[i]);
}
if ((strcmp(Prty[i],"Conservative")!=0) && (strcmp(Prty[i],"Labour")!=0))
{
printf("An invalid party was present in the list.");
}
}
printf ("Total Labour time in power: %d\nTotal Conservative time in power: %d\n", LabPwr, ConPwr);
}
This is the text file for the programme.
Attlee 7 1945 10 1951 Labour
Churchill 11 1951 5 1955 Conservative
Eden 6 1955 12 1956 Conservative
Macmillan 1 1957 10 1963 Conservative
Douglas-Home 11 1963 10 1964 Conservative
Wilson 11 1964 5 1970 Labour
Heath 6 1970 2 1974 Conservative
Wilson 3 1974 3 1976 Labour
Callaghan 4 1976 4 1979 Labour
Thatcher 5 1979 11 1990 Conservative
Major 12 1990 4 1997 Conservative
Blair 5 1997 6 2007 Labour
Brown 6 2007 5 2010 Labour
EDIT: I've just discovered if the size of every variable in Data is increased by one, the code runs without any of the issues. I assume this is some kind of overflow?
EDIT 2: Specifically if EndYr is [13] not [12] the problem is eliminated.

Answer 1

The word Conservative is 12 characters, but you must account for the null char '\0' at the end of every C string.
That is why your code works when you use 13 chars array for the Party field.
What you should do
Specify the maximum length of the Party field in the scanf format specifier. For example, if you keep 12 chars array for the party field:
fscanf(PriMins, "%s %d %d %d %d %11s", &PMs.Name[Max], &PMs.StrtMnth[Max], &PMs.StrtYr[Max], &PMs.EndMnth[Max], &PMs.EndYr[Max], &PMs.Party[Max])

Answer 2

You are reading 13 records from the file and have space to store only 12 of them as all you data items are of size 12.If you increase the size by 1 there is enough room for all 13 records
struct Data
{
char Name[13][15];
int StrtMnth[13];
int StrtYr[13];
int EndMnth[13];
int EndYr[13];
char Party[13][15];
int TimePwr[13];
};