在C中使用strcmp进行分段错误？

Question

I was getting Segmentation Fault (core dump) error when I run the code. After using some printf statement I found out that there is an error in strcmp part, maybe it's because comparing a char with a string? How do I fix this?

// this function checks if the file contains the *string

bool checkIfMatch(char *string, FILE *file) {

    while (true) {

        char buff[1024];
        fgets(buff, sizeof buff, file);
        if (buff == NULL)
            break;

        char *substring=strstr(buff, string);
        if ((strcmp(buff, substring)) == 0)
            return true;
    }

    return false;    
}

Answer 1

You have no guarantee that substring is non-NULL. So you need to test it:

bool checkIfMatch(char *string, FILE *file) {
    char buff[1024];
    while (fgets(buff, sizeof buff, file)) {
        char *substring=strstr(buff, string);
        if (substring && !strcmp(buff, substring)) 
            return true;
    }
    return false;
}

Other problems:

• In your code if (buff == NULL) break; will never cause a break. You need to test the return value of fgets . (See WhozCraig's comment)

• fgets keeps the carriage-return, which is probably not what you want.

• The strstr/strcmp is confused: you probably just want strcmp , or maybe just strstr .

• If the file has a line longer than 1022 characters, then you might miss finding the string.

Answer 2

The array buff is not null terminated. You need to do that for the str... family of functions

PS: Learn to indent the code PPS: Use a debugger to find of the value of buff

Answer 3

if the buff is not NULL terminated, then problem will come in the strcmp . In your case, initialize the buff variable(to zero) at the declaration part. Otherwise check the filesize and then add NULL character at the buff :

[filesize+1]='\0'.

Answer 4

char *substring=strstr(buff, string);
    if ((strcmp(buff, substring)) == 0)
        return true;

char *substring in the case where you have a match, substring is pointing to somewhere inside buf if no match substring is pointing to NULL , and when you do strcmp(buff,substring) this will never be zero.