如何根据c中的位置打印字符串？

Question

我正在研究一个问题，要求我在该位置给出给定为field-number的字符串。字符串应从文件中读取。

file.txt

C is a language.
lex lexical analyser
(blank line)
      gcc is good

如果field-number为2（即句子中的第二个单词）。该程序应输出

is
lexical
(NULL)
is

我编写了一个函数，但是认为它不是正确的方法，并且该函数在所有情况下都适用。它应该处理多余的空格或换行符。

while (fgets(buffer, MAX, file) != NULL) {
    for (int i = 1; i < strlen(buffer); i++) {
        if (count == field_number - 1) {
            int j = i;
            while (j < strlen(buffer) && buffer[j] != ' ') {
                printf("%c", buffer[j++]);
            }
            printf("\n");
            count = 0;
            break;
        }

        if (buffer[i] == ' ' && buffer[i - 1] != ' ') {
            count++;
        }
    }
}

我是初学者。该代码应易于理解。

Answer 1

这适用于所有情况，

int main() {
    //FILE* file = fopen(__FILE__, "r");
    //int field_number = 2;

    int new_line = 0; // var to keep track of new line came or not
    int word = 0;
    int count = 0;
    char c, prev_c;
    while ((c = fgetc(file)) != EOF) {
        // printf("[%c]", c);
        // if a new line char comes it means you entered a new line
        if(c == '\n') {
            // you have to print the new line here on the output to handle
            // empty line cases
            printf("\n");
            new_line = 1; // when line changes
            word = 0; // no word has come in this new line so far
            count = 0;    // count becomes 0
        } else if( c == ' ' && prev_c != ' ') {
            if(word)
                count++;
            if(count == field_number) // if count exceeds field_number
                new_line = 0; // wait till next line comes
        } else if (new_line && count == field_number - 1) {
            printf("%c", c);
        } else {
            word = 1; // fi a not new line or non space char comes, a word has come
        }
        prev_c = c;
    }
    return 0;
}

Answer 2

可以通过使用sscanf和%n和一个循环来迭代缓冲区。%n将捕获扫描处理的字符数。将所需迭代次数的每个scanned值添加到total中。

#include <stdio.h>

int main ( void) {
    char buffer[] = "C is a language.";
    char item[sizeof buffer] = "";
    int total = 0;
    int scanned = 0;
    int iterate = 2;

    for ( int each = 1; each < iterate; ++each) {
        scanned = 0;
        sscanf ( buffer + total, "%*s%n", &scanned);
        if ( ! scanned) {
            return 0;
        }
        total += scanned;
    }

    if ( buffer[total]) {
        sscanf ( buffer + total, "%s", item);

        printf ( "%s\n", item);
    }

    return 0;
}