Question

I am trying to get each line from a file and doing some string operations. But my piece of code throws seg fault. I tested the same thing for one line as a different program and it works fine. But when I read from a file and do string manipulation operations it throws me segmentation fault.

Variable declarations:

char *pch3,str1[100],str2[100]


 pch3 = strtok(line3,",");
                        while(pch3!=NULL)
                        {
                                if(strcmp(pch3,"?") == 0)
                                {
                                       strcat(str1,"0");
                                       strcat(str1,",");
                                }
                                else
                                {
                                       strcat(str1,pch3);
                                       strcat(str1,",");
                                }
                                pch3 = strtok(NULL,",");
                        }
                        strlen1=strlen(str1);
                        memcpy(str2,str1,strlen1-1);
                        fp2=fopen("breast-cancer-wisconsin-miscellaneous-cleansed.data","a");
                        fprintf(fp2,"%s\n",str2);
                        fclose(fp2);

Answer 1

You do not initialize str1 and str2, which means when you use strcat it tries to find the end of the previous string, but that can be anywhere in str1, even outside str1 if str1 does not contain a zero.

Change the declaration to this and it should work better:

char *pch3, str1[100] = "", str2[100] = "";