Let's say I have
char a[10], b[10], c[22];
Is there anyway I can copy the content of a and b to c?
I know how to copy one by one but I dont know how to copy more than 1 string.
Maybe I can do strlen(a), and strlen(b) and then do something like
for(n=0;n<strlen(a);n++){
c[n]=a[n];}
for(i=0;i<strlen(b),i++{
c[i+strlen(a)]=b[i];
c[strlen(a)+strlen(b)]='\0';}
Edit: I use the above method with some modification and I got it worked. However, it is kinda long.
is there any shorter way to do this?
Maybe std::string can help? You can copy the result into c if you want. Variables a and b can also still be arrays.
Code:#include <string>
std::string answer = a;
answer += b;
size_t len = answer.copy(c, sizeof(c) - 1);
c[len] = '\0';
This might be better accomplished byCode:size_t len = answer.copy(c, sizeof(c) - 1);
c[len] = '\0';
Code:if (sizeof(c) >= answer.size() + 1) // Make sure we don't get a buffer overrun!
strcpy(c, answer.c_str());
Or having gotten as far as using one std::string, why not use them for everything?
thx for the help guys. I ended up using this
std::string answer = a;
answer += b;
for(n=0;n<22;n++)
c[n]=answer[n];
c[n]='\0';
I dont understand this
size_t len = answer.copy(c, sizeof(c) - 1);
c[len] = '\0';
or this
if (sizeof(c) >= answer.size() + 1) // Make sure we don't get a buffer overrun!
strcpy(c, answer.c_str());
they dont give me the right answer
This is wrong. You copy 22 characters from answer into c, but there is no guarantee that answer has 22 characters. Furthermore, you add the null terminator to c[22], but c only has 22 characters, so c[22] does not exist (you wrote beyond the boundary of the array).Quote:
Originally Posted by byebyebyezzz
My question is the same as Salem's: having gotten as far as using one std::string, why not use them for everything?
Granted, there are situations when you must resort to a null terminated string, but thus far there is no sign of that.
It copes at most sizeof(c) - 1, i.e., 21, characters from answer into c, then adds the null terminator.Quote:
Originally Posted by byebyebyezzz
Similiar idea: there is a check that buffer overflow will not happen, then the null terminated string version of answer is copied to c.Quote:
Originally Posted by byebyebyezzz
It is your other code that is wrong. Pick either of the two and post the smallest and simplest compilable program that demonstrates the problem. Also, state what exactly is the answer that you get, and what is the answer that you expect. If there is external input, state what input you provided.Quote:
Originally Posted by byebyebyezzz
There's an overflow there, as laserlight points out. i == 22 after the loop.Quote:
Originally Posted by byebyebyezzz
If those don't work but the first solution does, you have done something wrong or left something out of what you posted here. The 2nd one uses the std::string method "copy" into c, the return value of which is the number of bytes copied. That's where you want the null terminator, since the copy method does not add one. This one might not work correctly if c is a pointer and not an array.Quote:
I dont understand this
size_t len = answer.copy(c, sizeof(c) - 1);
c[len] = '\0';
or this
if (sizeof(c) >= answer.size() + 1) // Make sure we don't get a buffer overrun!
strcpy(c, answer.c_str());
they dont give me the right answer
The 3rd one uses strcpy from <cstring>, which does append a null terminator. Either way, these should work. What is "wrong" about the answer you get?
No, that is not a problem since the null terminator only needs to be added once after the loop.Quote:
Originally Posted by MK27
Check, I misread that and corrected my post.Quote:
Originally Posted by laserlight
I ll post exactly what I have been doing. I already submit my assignment but I still want to learn how to improve my program.
This is a frunction in one of my class.
area, publisher, title and isbn are defined in class.Code:void ISBN::toStrWithStyle(char* str) const{
int n;
char str1[14];
std::string answer = area; // use of std::string to copy everything in 1 string.
answer += '-';
answer += publisher;
answer += '-';
answer += title;
answer += '-';
answer += isbn[9];
answer += '\0';
for(n=0;n<14;n++){
str1[n]=answer[n];}
str1[n]='\0';
if(registered==true){
strcpy(str,str1);
}
else
toStr(str);
If I use the other way, I get str = . or <.
isbn=1111111111
I want to get an out put that similar to this 11-1111-111-1
The total length for str will be 13. I set my n=14.
Once again, your writing beyond the last element in the array here: str1[n]='\0'; . Since you already put a null char at the end of answer, you can just remove this line.
There is no need for str1; you can write to str directly. Use strcpy(str, answer.data() ).
But let us ask why you are using C-style strings? Is it a requirement? Are you allowed to only use std::string? If not, is there a reason why you don't go pure std::string and avoid this madness?
AFAIK, data() is not guaranteed to null-terminate the string; hence this is dangerous. Use c_str() instead:Quote:
Originally Posted by King Mir
strcpy(str, area.c_str());
And don't forget to check for buffer overruns!
Yes, but answer += '\0' is guaranteed to null terminate it.Quote:
Originally Posted by Elysia
I don't know why I wrote area. It should be answer.