Copying and Merging two strings in C - c

Question

Note: Follow Alk's solution as a guide on your implemetation
I want to create a function that will let the user insert a directory where output files would be saved. My output files will have a static name so I just need the path.
I want to read the path from the user and append it before the name of the output file. So it would be like this:
output name (generated by another function) outLogFile = "outLogFile.log"
user input = D:\Datasets\some_folder\more_folders
RESULT = D:\Datasets\some_folder\more_folders\outLogFile.log
The way I am doing it, I insert the output name on a temp, use strcpy to copy the file path into outLogFile and strcat to append temp into outLogFile.
Is there a simpler way to do it? A way to merge the two strings into my outLogFile without the use of the temp? A single command to copy the string of path_file before the ouLogFile string, and save it into outLogFile?
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main ()
{
char user_input[100], *path_file,*temp;
char *outLogFile = "outLogFile.log";
printf("Filepath:\n (!Do not inlude filename!)\n");
gets(user_input);
path_file = (char*)malloc(strlen(user_input)+1);
if (user_input[strlen(user_input) - 1]!='\\')
{
strcpy(path_file, user_input);
strcat(path_file, "\\");
}
else
{
strcpy(path_file, user_input);
}
temp = outLogFile;
strcpy(outLogFile, path_file);
strcat(outLogFile, temp);
printf("%s\n%s\n", path_file,outLogFile);
system("pause");
return 0;
}
EDIT: I could use the user_input and path_file to malloc the outLogFile and strcpy strcat the string as follows
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main ()
{
char user_input[100];
char *outLogFile;
char *path_file = "outLogFile.log";
printf("Filepath:\n (!Do not inlude filename!)\n");
fgets(user_input,sizeof(user_input), stdin);
printf("%c\n",user_input[strlen(user_input) - 1]);
outLogFile = (char*)malloc(strlen(user_input)+strlen(path_file));
if (user_input[strlen(user_input) - 1]!='\\')
{
strcpy(outLogFile,user_input);
strcat(outLogFile, "\\");
strcat(outLogFile,path_file);
}
else
{
strcpy(outLogFile,user_input);
strcat(outLogFile,path_file);
}
printf("%s",outLogFile);
system("pause");
return 0;
}
However this code takes the \n by hitting the return button and inserts it between the two strings

Answer 1

To prefix a string by another string and store the result in a new string the most flexible generic approach would be to use dynamic memory allocation like this:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(void)
{
char * ps1 = "Hello";
char * ps2 = " World";
size_t length_total = strlen(ps1) + strlen(ps2);
char * ps3 = malloc((length_total + 1) * sizeof *ps3); /* One more for
the 0-terminator. */
if (NULL == ps3)
{
perror("malloc() failed");
exit(EXIT_FAILURE);
}
strcpy(ps3, ps1);
strcat(ps3, ps2);
/* Use ps3. */
puts(ps3);
/* Clean up. */
free(ps3);
return EXIT_SUCCESS;
}
In your particular case where the code provide a default filename without a path and the use-case is to allow prefixing the filename on run-time one might approach this in a simpler way like this.
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#define LOGFILENAME "some.log"
int main(void)
{
char logfilepath[PATH_MAX] = LOGFILENAME; /* Just to make sure. */
char dir[PATH_MAX] = "";
if (NULL == fgets(dir, sizeof dir, stdin))
{
if (ferror(stdin))
{
perror("fgets() failed");
exit(EXIT_FAILURE);
}
}
dir[strcspn(dir, "\n\r")] = 0;
{
size_t length_dir = strlen(dir);
if (length_dir > 0 && '/' != dir[length_dir - 1])
{
if (PATH_MAX < length_dir)
{
errno = EINVAL;
perror("'dir' to long");
exit(EXIT_FAILURE);
}
strcat(dir, "/");
++length_dir;
}
{
size_t length_total = length_dir + strlen(logfilepath);
if (PATH_MAX < length_total)
{
errno = EINVAL;
perror("'dir/filename' to long");
exit(EXIT_FAILURE);
}
}
}
strcpy(logfilepath, dir);
strcat(logfilepath, LOGFILENAME);
/* Use logfilepath, . */
puts(logfilepath);
return EXIT_SUCCESS;
}
To not trick this using the #define and to not use a third variable go for shifting:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
int main(void)
{
char logfilepath[PATH_MAX] = "some.log";
{
char dir[PATH_MAX] = "";
if (NULL == fgets(dir, sizeof dir, stdin))
{
if (ferror(stdin))
{
perror("fgets() failed");
exit(EXIT_FAILURE);
}
}
dir[strcspn(dir, "\n\r")] = 0;
{
size_t length_filepath = strlen(logfilepath);
size_t length_dir = strlen(dir);
if (length_dir > 0 && '/' != dir[length_dir - 1])
{
if (PATH_MAX < length_dir)
{
errno = EINVAL;
perror("'dir' to long");
exit(EXIT_FAILURE);
}
strcat(dir, "/");
++length_dir;
}
if (PATH_MAX < (length_dir + length_filepath))
{
errno = EINVAL;
perror("'dir/filename' to long");
exit(EXIT_FAILURE);
}
memmove(logfilepath + length_dir, logfilepath, length_filepath + 1);
memcpy(logfilepath, dir, length_dir);
}
}
/* Use logfilepath, . */
puts(logfilepath);
return EXIT_SUCCESS;
}

Answer 2

You may use sprintf() .
Following is the declaration for sprintf() function.
int sprintf(char *str, const char *format, ...)
For Example :
sprintf(outLogFile, "%s%s", path_file, outLogFile);
You have to care about '\0' character of first string now.