How to manipulate string properly in C - c

Question

I'm still new in C. I'm doing an enviroment variable task and I'm having a problem in processing my string. I would like to pass a variable that represent the environment variable, and replace a value that has ${...} with environment value if that string are same as the enviroment key. Here are the codes:
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
void replace_env(char *string, char *env)
{
int y = 0;
int x = 0;
int j = 0;
int i = 0;
int n = 0;
int val_length;
int location2[100];
char *tmp3[BUFSIZ];
char env_key[BUFSIZ];
char env_val[BUFSIZ];
char env_var[sizeof(env)][BUFSIZ];
char user_input[BUFSIZ];
char final_string[BUFSIZ];
char tmp_key[100][BUFSIZ];
tmp3[x]=env;
strncpy(env_var[x],tmp3[x],sizeof(tmp3));
for(x=0;env_var[y][x] != '=';x++) //this is to get the environment key
{
env_key[x] = env_var[y][x];
}
x++;
for(j=0;env_var[y][j] != '\0';j++) //this is to get the environment value
{
env_val[j]=env_var[y][x];
x++;
}
val_length = strlen(env_val);
j=0;
y=0;
strncpy(user_input,string,sizeof(user_input));
for(x = 0;user_input[x] !='\0';x++)
{
if (user_input[x] =='$')
{
x++;
if(user_input[x] == '{')
{
x++;
y=0;
while(user_input[x]!='}')
{
tmp_key[i][y] = user_input[x];
x++;
y++;
}
i++;
}
}
}
tmp_key[i][y]='\0';
i=0;
for(x = 0;user_input[x] !='\0';x++) //I think my problem is starting from here.
{
if (user_input[x] !='$')
{
final_string[j]=user_input[x];
j++;
}
else
{
x++;
if((user_input[x]== '{')&&(strncmp(tmp_key[i],env_key,sizeof(tmp_key))==0))
{
while(user_input[x]!='}')
{
x++;
}
strcat(final_string,env_val);
j=j+val_length;
}
else
{
final_string[j]=user_input[x];
j++;
}
}
}
printf("output result = %s \n",final_string);
}
int main() {
char s[100];
sprintf(s, "jack${ABC}zack${DEF}");
replace_env(s, "ABC=/home/fikrie/Documents");
replace_env(s, "DEF=/tmp");
if (strcmp(s, "jack/home/fikrie/Documentszack/tmp")==0) {
printf("pass\n");
} else {
printf("fail\n");
}
printf("--------------------------------------------------------\n");
return 0;
}
To make it more clearer, here are the result:
env_var = ABC=/home/fikrie/Documents
env_key = ABC
env_val = /home/fikrie/Documents
input = jack${ABC}zack${DEF}
after strcat result is = jack/home/fikrie/Documents
j value is 26
after strcat result is = jack/home/fikrie/Documentszack/home/fikrie/Documents
j value is 52
output result = jack/home/fikrie/Documentszack/home/fikrie/Documents
env_var = DEF=/tmp
env_key = DEF
env_val = /tmp
input = jack${ABC}zack${DEF}
output result = jack{ABC}zack{DEF}ocumentszack/home/fikrie/Documents
fail
--------------------------------------------------------
As you can see, ABC are sent into the replace_env function. And it does replace the ${ABC} properly, followed with a string zack.Then the problem occures where ${DEF} are replaced with ABC key and not maintained as ${DEF}
When the DEF are sent during the second call of replace_env function, things got more wierd. Both ABC and DEF are not recognized. Even worse, the character at the back are still there.
My expectation is:
For the first call of replace_env:
jack/home/Fikrie/Documentszack${DEF}
For the second call of replace_env:
jack/home/Fikrie/Documentszacl/tmp
after the strcmp passed, the final_string will be cleared again.
All help are really appreciated. I dont expect an answer. I prefer a knowledge or guidance rather than just solving it blankly. Just need a clear explanation on my fault because I have been editing this code for almost a month and everything looks so blurry now. I know there are ways to solve it using memory functions, allocation etc. But this task is about string manipulation. I am running this on Ubuntu OS. Sorry for my bad english.

Answer 1

I know you didn't ask for this, but consider this. Learning the C string functions is worth your time.
#include <stdio.h>
#include <string.h>
void sub(char *s, char *env, char *value) {
char buf[BUFSIZ], *src = s, *dst = buf;
int n = strlen(env);
while(*src) {
if(strncmp(src, env, n) == 0) {
dst += strlen(strcpy(dst, value));
src += strlen(env);
} else {
*dst++ = *src++;
}
}
*dst = 0;
strcpy(s, buf);
}
void replace_env(char *s, char *env) {
char copy[BUFSIZ], tmp[BUFSIZ];
strcpy(copy, env);
char *eq = strchr(copy, '=');
if(eq == 0) {
printf("No '=' found in '%s'\n", env);
return;
}
*eq = 0;
sprintf(tmp, "${%s}", copy);
sub(s, tmp, eq+1);
}
int main() {
char s[100];
sprintf(s, "jack${ABC}zack${DEF}");
replace_env(s, "ABC=/home/fikrie/Documents");
replace_env(s, "DEF=/tmp");
if (strcmp(s, "jack/home/fikrie/Documentszack/tmp")==0) {
printf("pass\n");
} else {
printf("fail\n");
}
printf("--------------------------------------------------------\n");
return 0;
}