Question

I trying to do some very basic string processing in C (e.g. given a filename, chop off the file extension, manipulate filename and then add back on the extension)- I’m rather rusty on C and am getting segmentation faults.

char* fname;
char* fname_base;
char* outdir;
char* new_fname;
.....
fname = argv[1];
outdir = argv[2];
fname_len = strlen(fname);
strncpy(fname_base, fname, (fname_len-4)); // weird characters at the end of the truncation?
strcpy(new_fname, outdir); // getting a segmentation on this I think

strcat(new_fname, "/");
strcat(new_fname, fname_base);
strcat(new_fname, "_test");
strcat(new_fname, ".jpg");
printf("string=%s",new_fname);  

Any suggestions or pointers welcome.

Many thanks and apologies for such a basic question

Answer 1

You need to allocate memory for new_fname and fname_base. Here’s is how you would do it for new_fname:

new_fname = (char*)malloc((strlen(outdir)+1)*sizeof(char));

In strlen(outdir)+1, the +1 part is for allocating memory for the NULL CHARACTER '\0' terminator.