How to make a string buffer...

[s88]

Hello All:
I'm trying to make a string buffer for my APIs. For example:
void test(char * str){
sprintf(str,"inner test\n");

}

int main(void){
int i = -5;
char *str=(char*)malloc(sizeof(char)*100);
sprintf(str,"\number is %d\n",i);
test(str);
printf("STR IS %s\n",str);
return 0;
I want the char array str contains "\nnumber is -5\ninner test\n", but
the result is "\ninner test\n". I know the str means that the beginning
pointer of the cahr array. So, as I invoke the test function, the
sprintf of teh test function write down the characters from the
beginning of the str.
How to slove this problem?
Thank you!

Dave.

[Sandeep]

s88 wrote:

Hello All:
I'm trying to make a string buffer for my APIs. For example:
void test(char * str){
sprintf(str,"inner test\n");

}

int main(void){
int i = -5;
char *str=(char*)malloc(sizeof(char)*100);
sprintf(str,"\number is %d\n",i);
test(str);
printf("STR IS %s\n",str);
return 0;
I want the char array str contains "\nnumber is -5\ninner test\n", but
the result is "\ninner test\n". I know the str means that the beginning
pointer of the cahr array. So, as I invoke the test function, the
sprintf of teh test function write down the characters from the
beginning of the str.
How to slove this problem?

Not sure what you mean by "String Buffer", but if this is a specific
problem, you can just use strcat in "temp" function.

void test(char * str)
{
strcat(str," inner test\n");
}

[Robert Gamble]

s88 wrote:

Hello All:
I'm trying to make a string buffer for my APIs. For example:
void test(char * str){
sprintf(str,"inner test\n");

}

int main(void){
int i = -5;
char *str=(char*)malloc(sizeof(char)*100);
sprintf(str,"\number is %d\n",i);
test(str);
printf("STR IS %s\n",str);
return 0;
I want the char array str contains "\nnumber is -5\ninner test\n", but
the result is "\ninner test\n". I know the str means that the beginning
pointer of the cahr array. So, as I invoke the test function, the
sprintf of teh test function write down the characters from the
beginning of the str.
How to slove this problem?

Don't cast the return value of malloc and check out the strcat
function.

Robert Gamble

[CBFalconer]

Robert Gamble wrote:

s88 wrote:

I'm trying to make a string buffer for my APIs. For example:
void test(char * str){
sprintf(str,"inner test\n");
}

int main(void){
int i = -5;
char *str=(char*)malloc(sizeof(char)*100);
sprintf(str,"\number is %d\n",i);
test(str);
printf("STR IS %s\n",str);
return 0;
}

I want the char array str contains "\nnumber is -5\ninner test\n",
but the result is "\ninner test\n". I know the str means that the
beginning pointer of the cahr array. So, as I invoke the test
function, the sprintf of teh test function write down the
characters from the beginning of the str.
How to slove this problem?

Don't cast the return value of malloc and check out the strcat
function.

Better, check out the (non-standard) strlcpy and strlcat
functions. You can find an implementation in pure portable C, with
references to the original proposals, etc., at:

<http://cbfalconer.home.att.net/download/strlcpy.zip>

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