question about strcat() in C

thungmail · 11-07-2009, 02:47 AM

Code:

int main()
{
   
   char* date1="Dec 29, 8:30";
   char* date2="Dec 28, 7:30";
   char* year =" 2009";
   strcat(date1,year);      
   strcat(date2,year);
   return 0;
}

After compiling and executing, the compiler gives an error

Code:

red 312 % time.out
Segmentation fault

After looking at the function strcat(), it takes 2 args of type of pointer and it is what i am passing to strcat(). I dont know i got the error. I need a explanation for it.
Thanks

Brain_Child · 11-07-2009, 03:20 AM

strcat adds on the second string to the end first string. so you have to leave some space at the end of the first string. for example

Code:

   char date1[20]="Dec 29, 8:30";
   char date2[20]="Dec 28, 7:30";
   char* year =" 2009";
   strcat(date1,year);
   strcat(date2,year);
   printf("%s\n%s\n", date1, date2);

date1 is an array that has a bit of room left over at the end. same with date2. so you can use strcat now since there is room to add year on the end

Dino · 11-07-2009, 06:57 AM

Also, when declaring strings like that, your compiler may mark those strings to be placed into read-only memory when the program is loaded, and thus adding more room to them to do a strcat() later might be a fruitless effort.

11-07-2009, 02:47 AM	#1
thungmail Registered User Join Date: Mar 2008 Posts: 39	question about strcat() in C Code: int main() { char* date1="Dec 29, 8:30"; char* date2="Dec 28, 7:30"; char* year =" 2009"; strcat(date1,year); strcat(date2,year); return 0; } After compiling and executing, the compiler gives an error Code: red 312 % time.out Segmentation fault After looking at the function strcat(), it takes 2 args of type of pointer and it is what i am passing to strcat(). I dont know i got the error. I need a explanation for it. Thanks
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11-07-2009, 03:20 AM	#2
Brain_Child Registered User Join Date: Feb 2009 Posts: 35	strcat adds on the second string to the end first string. so you have to leave some space at the end of the first string. for example Code: char date1[20]="Dec 29, 8:30"; char date2[20]="Dec 28, 7:30"; char* year =" 2009"; strcat(date1,year); strcat(date2,year); printf("%s\n%s\n", date1, date2); date1 is an array that has a bit of room left over at the end. same with date2. so you can use strcat now since there is room to add year on the end
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11-07-2009, 06:57 AM	#3
Dino Jack of many languages Join Date: Nov 2007 Location: Katy, Texas Posts: 1,929	Also, when declaring strings like that, your compiler may mark those strings to be placed into read-only memory when the program is loaded, and thus adding more room to them to do a strcat() later might be a fruitless effort. __________________ Mac and Windows cross platform programmer. Ruby lover. Memorable Quotes From Recent Posts: I can't remember.
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