See this code:
int main() {
char a[50];
FILE *fp;
fp = fopen("test1.txt", "w");
sprintf(a,"jigar %d \n", 3);
fprintf(fp,"jigar %d \n", 3);
sprintf(a,"patel %d \n", 2);
fprintf(fp,"patel %d \n", 2);
printf("%s", a);
}
Here, using fprintf, I can write in file
jigar 3
patel 2
where same functionality I want where what ever I print that goes in one char buffer.
but using sprintf gives me on buffer
patel 2
I have so many such print which I want to add in one char buffer and then I need to return it to application so how to get it in simplest and fastest way this?
sprintf() returns the number of characters printed.
Just use that number for the next write ...
int i;
char a[50];
char *ap = a;
for (i = 5; i < 15; i++) {
ap += sprintf(ap, "%d ", i);
}
printf("%s\n", a); /* "5 6 7 8 9 10 11 12 13 14 " */
Make sure you don't cause any buffer overflows though.
The idea is to give sprintf the pointer to the base address of your buffer + an offset. The offset gets bigger while you are appending.
By using strlen it is possible to get the lenght of the current 'string'.To avoid a buffer overflow, we could add extra logic in order to check if the current 'string' + 'the new string' is less than the size of the buffer.
size_t offset = strlen(text);
sprintf(&(text[offset]), "This is how You append using sprintf");
Example within a loop:
char text[255];
text[0] = '\0';
for(int i = 0 ; i < 10 ; i++) {
size_t offset = strlen(text);
sprintf(&(text[offset]), "%d,", i);
}
As from other stackoverflow users suggested, you could also use snprintf, which would give you also buffer overflow protection.
An append function could look like this:
void append(char *text, int maxSize, char *toAppend) {
size_t offset = strlen(text);
snprintf(&(text[offset]), maxSize, "%s", toAppend);
}
If you're on a POSIX-compatible system, have a look at fmemopen(3) or open_memstream(3):
#include <assert.h>
#include <stdio.h>
int main(void)
{
char buf[128] = { 0 };
FILE *fp = fmemopen(buf, sizeof(buf), "w");
assert(fp);
fprintf(fp, "Hello World!\n");
fprintf(fp, "%s also work, of course.\n", "Format specifiers");
fclose(fp);
puts(buf);
}
