How to concatenate char and string / How to make char to string - c

Question

#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#define MAX_SIZE 20
void main()
{
int i, j;
char *str1, *str2, *str3, *str_mid;
bool **lcs1, **lcs2;
int len1, len2, len3, len_mid;
char *ch = (char*)malloc(sizeof(char) * 3);
str1 = (char*)malloc(sizeof(char)*MAX_SIZE); //applicatian
str2 = (char*)malloc(sizeof(char)*MAX_SIZE); //apiasn
str3 = (char*)malloc(sizeof(char)*MAX_SIZE); //apun
str_mid = (char*)malloc(sizeof(char)*MAX_SIZE); //apn
str_mid = "";
scanf("%s", str1);
scanf("%s", str2);
scanf("%s", str3);
len1 = strlen(str1);
len2 = strlen(str2);
len3 = strlen(str3);
//str2, str3 ->str_mid (lcs1)
lcs1 = (bool**)malloc(sizeof(bool*)*(len3 + 1));
for (i = 0; i < len3 + 1; i++)
lcs1[i] = (bool*)malloc(sizeof(bool)*(len2 + 1));
for (i = 0; i < len3 + 1; i++)
for (j = 0; j < len2 + 1; j++)
lcs1[i][j] = false;
for (i = 1; i < len3 + 1; i++)
for (j = 1; j < len2 + 1; j++)
if (str3[i-1] == str2[j-1])
lcs1[i][j] = true;
for (i = 1; i < len3 + 1; i++)
{
for (j = 1; j < len2 + 1; j++)
if (lcs1[i][j])
{
//<--- error
ch = str3[i - 1];
strcat(str_mid, ch);
//--->
break;
}
}
//printf("%s", str_mid);
//str_mid, str1 (lcs2)
}
In <--- error ---> part,
I want to concatenation str3[i-1] and str_mid but, str3[i-1] is character type.
So make temporary string is ch and do concatenate.
But, the access error is occurred.
How to make char to string or, how to concatenate char and string?

Answer 1

So long as MAX_SIZE is large enough that str_mid will be able to hold the extra character, you can use strcat() and a compound literal (for C99 or later):
strcat(str_mid, (char[2]){ str3[i - 1], '\0' });
Note that in your code, str3[i - 1] is a char, while you have declared ch as a pointer to char.

Answer 2

How to concatenate char and string
There is no need to call any library function at all, nor to dynamically allocate any memory.
Assuming str_mid is large enough just do:
{
size_t tmp_len = strlen(str_mid);
str_mid[tmp_len] = str3[i - 1];
str_mid[tmp_len + 1] = '\0';
}
To still have the feeling to use a function you might want to wrap the above code into a macro like this:
#define STRCATCHAR(s, c) \
do { \
assert(s != NULL); \
size_t tmp_len = strlen(s); \
(s)[tmp_len] = (c); \
(s)[tmp_len + 1] = '\0'; \
} while (0)
and use it like this:
STRCATCHAR(str_mid, str3[i - 1]);

Answer 3

To concatenate char and string (first char, then string) do:
const char* conc_char_string(const char ch, const char* str, int len) {
const char* out = malloc(len + 2); /* 1 char from ch, len chars from str, and zero character, totally len+2 */
out[0] = ch; /* copy the character */
strcpy(out+1, str); /* copy the string */
return out;
}
Here len should be strlen(str)

Answer 4

The statement str_mid = ""; assigns the address of costant string "" to pointer str_mid, which will cause segmentfault later. Use str_mid[0] = '\0'; instead.
In statement ch = str3[i - 1];, you are assigning char to char pointer, which will cause segmentfault.
If all you want is simply appending a character to the string, you can keep track of length of string, like this:
len_mid = strlen(str_mid);
for (i = 1; i < len3 + 1; i++)
{
for (j = 1; j < len2 + 1; j++)
if (lcs1[i][j])
{
str_mid[len_mid++] = str3[i - 1];
str_mid[len_mid] = '\0';
break;
}
}

Answer 5

First rule of the C-club, create your own string buffer, second rule of the C-club create your own string buffer.
Each programmer has it's own string buffer. Minimal requirement is :
#define STRINGSTRTSZ 256
typedef struct string
{
char *str;
size_t n;
size_t buf_sz;
}String,*pString;
pString new_string()
{
pString res;
res=malloc(sizeof(String)); ///i leave to you the error handling
res->bus_sz=STRINGSTRSZ;
res->n=0;
res->str=malloc(res->bus_sz);
}
char*concatbase(pString *string,char*s,size_t len)
{
if(len+1>=string->buf_sz-string->n)
{
res->buf_sz+=len+res->buf_sz;
char *tmp=realloc(string->str,res->buf_sz);
if(tmp)
string->str=tmp;
else
...
}
memcpy(string->str+string->n,s,len);
string->n+=len;
*(string->str+string->n)='\0';
return string->str;
}
#define concatNllPtr(string,nllptr) concatbase(string,nllptr,strlen(nllptr))
#define concatString(string,str2) concatbase(string,(str2)->str,(str2)->n)
End so on...