未初始化的值使用，使用 sprintf 或 strcat 时出错

Question

The piece of code given below works completely fine on my IDE. But when I submit this on codeforces , I get an error pointing at the sprintf line.

Probably, the solution is executed with error 'uninitialized value usage'

I used sprintf instead of strcat to concatenate two arrays as suggested from a stackoverflow answer. But it gives me the same error.

char a[101],b[101],c[201],d[300];
fgets(a,101,stdin);
fgets(b,101,stdin);
fgets(c,201,stdin);
// strcat(d,a);
sprintf(d, "%s%s",d,a);

Answer 1

You are writing the uninitialized variable d to the location d . That doesn't make any sense. Perhaps you meant to do sprintf(d,"%s",a); ?

In that case you don't need to initialize d , but if you use strcat you must initialize the first item in d to \0 .

Answer 2

You can only use strcat() if you've already initialized both strings.

Since you haven't put anything into d yet, you don't need to concatenate to it. Just copy the contents of a to it with strcpy() .

strcpy(d, a);

Also, even if you have initialized d, you can't use

sprintf(d, "%s%s",d,a);

It's not valid to use the same string as the destination of sprintf() if it's also one of the source strings.

Answer 3

You have not initialized d so it probable has no '\0' character.

strcat searches for the first 0 in the array and then starts concatenting from there. If it cant find a 0 it read past the end of the array.

char d[300] = {0};

would fix it both for strcat and sprintf