linux c 修改文件某一行的值代码示例

在Linux环境下，使用C语言直接修改文件内容通常涉及到文件I/O操作，特别是当文件较大并且需要处理行级别的数据时，可以采用逐行读取、修改后再写回的方式。这里有一个简单的示例，假设我们要修改一个文本文件中的特定行：

#include <stdio.h>
#include <stdlib.h>

#define MAX_LINE_LENGTH 100

void replace_line_in_file(const char *filename, int line_num, const char *new_content) {
    FILE *file = fopen(filename, "r+");
    if (file == NULL) {
        perror("Failed to open file");
        return;
    }

    char line[MAX_LINE_LENGTH];
    size_t line_count = 0;

    while (!feof(file)) {
        size_t bytes_read = fread(line, sizeof(char), MAX_LINE_LENGTH, file);
        if (bytes_read > 0 && fgets(line + bytes_read, MAX_LINE_LENGTH - bytes_read, file) != NULL) { // Read a line
            ++line_count;

            // If we found the line to modify
            if (line_count == line_num) {
                fseek(file, 0, SEEK_SET); // Reset position to beginning of the file
                fprintf(file, "%s", new_content); // Write the new content
                fseek(file, 0, SEEK_END); // Go back to end after writing
                break; // We don't need to read further
            }
        } else {
            break;
        }
    }

    fclose(file);

    if (line_count < line_num) {
        printf("Line %d not found.\n", line_num);
    }
}

// 使用示例
int main() {
    const char *filename = "test.txt";
    int line_number_to_replace = 5;
    char new_line[] = "New value for this line";

    replace_line_in_file(filename, line_number_to_replace, new_line);