#include <stdio.h>

int main (int argc, char *argv[])
{
    char *stringOne="Строка один";
    char *stringTwo="Строка два";
    int resultStringSize=strlen(stringOne)+strlen(stringTwo)+1;
    char resultString[resultStringSize];
    int charIndex=0;
    char nowCharacter=-1;
    int i=0;
    while (1)
    {
        nowCharacter=stringOne[i];
        if (nowCharacter==0) break;
        resultString[charIndex]=nowCharacter;
        charIndex++;
        i++;
    }
    i=0;
    nowCharacter=-1;
    while (1)
    {
        nowCharacter=stringTwo[i];
        if (nowCharacter==0) break;
        resultString[charIndex]=nowCharacter;
        charIndex++;
        i++;
    }
    resultString[charIndex]=0;
    printf("%s\n",resultString);
    return 0;
}

#include <string>
int main() {
    std::string s;
    std::string c = "_";
    for(int i = 0; i < 100000000; ++i) {
        c[0] = (char)((i % 94)+32);
        s += c;
    }
    printf("%s\n", s.c_str());
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
  char *s;
  int len = 0;
  int i;
  char c;
  for(i = 0; i < 100000000; ++i) {
    if(i == 0) {
      len = 2 *(i+1);
      s = malloc(len);
    }
    if(i >= len) {
      len = 2 *(i+1);
      char *t = realloc(s, len);
      s = t;
    }
//  s[i] = (i % 94)+32; would be faster, but we want to test concatenation
    c = (i % 94)+32;
    strncat(s+i, &c, 1);
  }
  s[i] = '\0';
  printf("%s\n", s);
  return 0;
}

% gcc test.c -o testc -O2                
% g++ test.cpp -o testcpp --std=c++11 -O2
% time ./testc > /dev/null               
./testc > /dev/null  1.51s user 0.20s system 100% cpu 1.714 total
% time ./testc > /dev/null
./testc > /dev/null  1.52s user 0.04s system 100% cpu 1.562 total
% time ./testc > /dev/null
./testc > /dev/null  1.24s user 0.03s system 100% cpu 1.264 total
% time ./testc > /dev/null
./testc > /dev/null  1.23s user 0.10s system 100% cpu 1.324 total
% time ./testc > /dev/null
./testc > /dev/null  1.24s user 0.03s system 100% cpu 1.262 total
% time ./testcpp > /dev/null
./testcpp > /dev/null  1.32s user 0.20s system 100% cpu 1.522 total
% time ./testcpp > /dev/null
./testcpp > /dev/null  1.07s user 0.08s system 100% cpu 1.154 total
% time ./testcpp > /dev/null
./testcpp > /dev/null  1.32s user 0.16s system 100% cpu 1.484 total
% time ./testcpp > /dev/null
./testcpp > /dev/null  1.07s user 0.14s system 99% cpu 1.214 total
% time ./testcpp > /dev/null
./testcpp > /dev/null  1.08s user 0.13s system 100% cpu 1.204 total

cat 1.cpp
#include <string>
int main() {
    std::string s;
    std::string c = "_";
    for(int i = 0; i < 100000000; ++i) {
        c[0] = (char)((i % 94)+32);
        s += c;
    }
    printf("%s\n", s.c_str());
}

cat 1.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BLOCK_SZ 1024

int main() {
  char *s, *cptr;
  size_t len = BLOCK_SZ;
  int i;
  if(!(s = malloc(BLOCK_SZ))) return -1;
  cptr = s;
  for(i = 0; i < 100000000; ++i){
    if(i == len){
      len += BLOCK_SZ;
      if(!(s = realloc(s, len))) return -1;
      cptr = s + i;
    }
    *cptr++ = (i % 94) + 32;
  }
  *cptr = 0;
  printf("%s\n", s);
  return 0;
}

gcc 1.c -o testc -O2
g++ 1.cpp -o testcpp --std=c++11 -O2

time for i in $(seq 1 10); do ./testcpp > /dev/null; done

real	0m16.128s
user	0m14.853s
sys	0m1.179s

time for i in $(seq 1 10); do ./testc > /dev/null; done

real	0m4.744s
user	0m4.052s
sys	0m0.665s

% time ./testc > /dev/null
./testc > /dev/null  0.30s user 0.03s system 99% cpu 0.334 total
% time ./testc > /dev/null
./testc > /dev/null  0.37s user 0.25s system 100% cpu 0.616 total
% time ./testc > /dev/null
./testc > /dev/null  0.37s user 0.04s system 99% cpu 0.409 total
% time ./testc > /dev/null
./testc > /dev/null  0.31s user 0.22s system 99% cpu 0.531 total
% time ./testc > /dev/null
./testc > /dev/null  0.30s user 0.16s system 99% cpu 0.460 total
% time ./testc > /dev/null
./testc > /dev/null  0.38s user 0.04s system 99% cpu 0.415 total

s[i] = ...

text1=open(file1).read()
text2=open(file2).read()
print(len(text1+text2))

cat 2.c 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

char *strconcat(char *a, char *b){
	size_t La, Lb, Ltot;
	La = strlen(a);
	Lb = strlen(b);
	Ltot = La + Lb;
	a = realloc(a, Ltot+1);
	if(!a) return NULL;
	memcpy(a, b, Lb);
	a[Ltot] = 0;
}

char *genrandstr(int L){
	int i;
	char *ret = malloc(L+1);
	if(!ret) return NULL;
	for(i = 0; i < L; i++){
		ret[i] = 32 + (rand() % 95);
	}
	ret[L] = 0;
	return ret;
}

int main(){
  char *s;
  int i;
  srand(time(NULL));
  s = genrandstr(rand() % 1024 + 10);
  if(!s) return -3;
  for(i = 0; i < 100000; ++i){
    char *randstr = genrandstr(rand() % 2048 + 10);
    if(!randstr) return -1;
    if(!(s = strconcat(s, randstr))) return -2;
    free(randstr);
  }
  printf("%s\n", s);
  return 0;
}

gcc -O2 2.c -o teststrconcat
time for i in $(seq 1 10); do ./teststrconcat > /dev/null; done

real	0m13.878s
user	0m13.805s
sys	0m0.010s

char *
getrnd()
{
        char a[] = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
        int n = arc4random() % sizeof(a);
        char *r;
        asprintf(&r, "%.*s", n, a);
        return r;
}

cat 2.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

char *strconcat(char *a, char *b){
	size_t La, Lb, Ltot;
	La = strlen(a);
	Lb = strlen(b);
	Ltot = La + Lb;
	a = realloc(a, Ltot+1);
	if(!a) return NULL;
	memcpy(a+La, b, Lb);
	a[Ltot] = 0;
	return a;
}

char *genrandstr(int L){
	int i;
	char *ret = malloc(L+1);
	if(!ret) return NULL;
	for(i = 0; i < L; i++){
		ret[i] = 32 + (rand() % 95);
	}
	ret[L] = 0;
	return ret;
}

int main(){
  char *s;
  int i;
  srand(time(NULL));
  s = genrandstr(rand() % 1014 + 10);
  if(!s) return -3;
  for(i = 0; i < 1000; ++i){
    char *randstr = genrandstr(rand() % 1014 + 10);
    if(!randstr) return -1;
    if(!(s = strconcat(s, randstr))) return -2;
    free(randstr);
    printf("got: %s\n\n",s);
  }
  printf("%s\n", s);
  return 0;
}

gcc -O2 2.c -o teststrconcat
time for i in $(seq 1 10); do ./teststrconcat > /dev/null; done

real	0m4.401s
user	0m4.366s
sys	0m0.014s