Hi,
My program takes two (filename) arguments, and I want the second argument to change to filename2C.dat
[slippy@slipnslidn ~]% ./program filename1.dat filename2.dat
Thanks for your help.Code:FILE* fn, fm, fo; int main(int* argc, char** argv){ fn = fopen(argv[1], "r"); fm = fopen(argv[2], "r"); /* This doesn't work... */ fo = fopen(strcat(strstr(argv[2], "."), "C.dat", "w")); /* Do something */ /* Shut things down */ close(fn); close(fm); close(fo); }
You should copy the command-line argument to a temp buffer and work on that, not on the argument directly. Aside from that, the strcat should probably be a strcpy instead and one of the right parenthesis is in the wrong place... it should be after the "C.Dat" string and not after the "w".
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> strcat(strstr(argv[2], "."), "C.dat", "w")
Split this out into it's component steps.
For starters, strstr() can return NULL, which leaves you up the creek without a paddle.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
That won't work because it uses memory improperly. You need to allocate enough space for the string and built it yourself:
Code:#include <string.h> #include <stdlib.h> #include <stdio.h> char *dot, *newname; int len; /* Get position of the last dot in the name */ dot = strrchr(name, '.'); /* If a dot was found, calculate the length to this point */ if(dot) len = dot - name; else len = strlen(name); /* Allocate a buffer big enough to hold the result. * 6 extra characters: 5 for "C.dat", 1 for null byte */ newname = malloc(len + 6); /* Build the new name */ strncpy(newname, name, len); strcpy(newname + len, "C.dat");
