Question

I am just attempting to concatenate two strings in C and I don’t know why but I’m getting segfault errors. I tracked it down using gdb to the first line in the lines of code below.

  strcat(tempString, "uptime");
  pFile = fopen (tempString,"r");

tempString is = “/proc/”. I just want to append the string “uptime” to the tempString and then attempt to open the file if it exists in the /proc folder. When memcpy() is called by strcat() is when the actual segfault occurs.

Answer 1

You have not shown some code before these lines, but it is likely tempString is assigned using

tempString = "/proc/";

Which makes it a constant (with constant mem size allocation)
The 2nd line strcat will atempt to overwrite the string constant, which puts 6 bytes beyond your buffer into unknown territory (*if it succeeded).

Use strcat responsibly: http://beej.us/guide/bgc/output/html/multipage/strcat.html

* as JeremyP points out, if it points to the text segment, it is read only and will cause the segfault