C编程：gets（）和Char String Array问题 - strcpy（）复制到Array中的其他字符串

Question

I am using the function gets() to retrieve string input from the user. I then store that string into a char array, char transdestmp[DESMAX], where DESMAX is 31. If the variable_name is greater than 30 chars, then ask the user to renter another string. Else, copy the string using strcpy(), into a 2 dimensional array char - acctdes[31][20].

accttitle recieves transdestmp[DESMAX]

void accttitle(char descr[DESMAX])
{
    printf("\nEnter title for new account %d: ", transinpt);
    gets(descr);
    while(strlen(descr)>DESMAX){
        printf(" **Title entered is longer than 30 characters\n");
        printf(" Please reenter : ");
        gets(descr);
    }
    strcpy(acctdes[transcntr],descr);
    printf("---->vacctdes[transcntr]: %s\n", acctdes[transcntr]);
    printf("---->vacctdes[transcntr-1]: %s\n", acctdes[transcntr-1]);
}

For some reason when I input a long string, and then enter another string, apart of the second string acctdes[1] overwrites the other string stored in acctdes[0].

for example,

First input: acctdes[0] = "This is a long string"

It works...

Second input acctdes[1] = "monkey"

It works...

but then, it seems that when I output acctdes[0], acctdes[0] has some of the value from acctdes[1]... like output - This is a long monk...

Please let me know if you would like more information. Thanks in advance.

Answer 1

Your array declaration should be other way round.

Currently you have : acctdes[31][20] , which means 31 place holders for 20 char length each; while you want 20 placeholders for 31 char length each.

It should be changed to acctdes[20][31]

Answer 2

"I am using the function gets() to retrieve string input from the user."

That's your problem, or at least part of it.

Never use the gets() function. It is inherently unsafe unless you have complete control over what input will appear on stdin . It has no mechanism to specify how many characters of input will be accepted. If the user enters more data than will fit in the target array, your program's behavior is undefined.

Use fgets() instead; it takes an argument specifying the size of the target buffer. You'll still have to deal with the possibility that the input line is too long (in that case, fgets() just stores a partial line). If the input line isn't too long, fgets() leaves the '\\n' in the buffer, unlike gets() .

It's so bad that it's been removed from the latest (2011) ISO C standard.

(See also the other answers.)

Answer 3

You have the dimensions on your array reversed. Try acctdes[20][31] .

The reason the strings bleed into each other is because C lays out a two-dimensional array as one long block of memory. When you do acctdes[2] its really doing pointer arithmetic under the hood like *(acctdes + (31 * 2)) to skip over the first part of the memory block to get to your third element. So if one string writes past its bounds, it will end up in the next string.