C语言程序读取结构体文件时strcmp匹配失败，请求技术支持

核心问题原因 #

你的代码和文件存储格式完全不匹配，导致strcmp无法匹配目标名字：

• 代码中使用fread/fwrite进行二进制读写，但实际employee.txt是纯文本格式。用二进制读取文本内容时，结构体emp.name会被填充一堆乱码，自然无法和输入的名字匹配。
• 额外隐患：gets函数会读取输入末尾的换行符到缓冲区，即使格式正确，也可能导致名字末尾多一个换行符，引发匹配失败。

解决方案 #

根据你的现有文件格式，有两种修正方向：

方向1：将文件转为二进制存储（适合批量结构化数据） #

先编写一个二进制写入程序，生成正确的二进制格式文件：

#include <stdio.h>
#include <string.h>

struct Employee {
    int id;
    char name[50];
    float salary;
};

int main() {
    FILE *file = fopen("employee.txt", "wb");
    if (!file) {
        perror("Failed to open file");
        return 1;
    }
    struct Employee emps[] = {
        {1, "aayush", 4000.0f},
        {2, "aashish", 3000.0f}
    };
    fwrite(emps, sizeof(struct Employee), 2, file);
    fclose(file);
    return 0;
}

然后修改原更新程序，替换不安全的gets并处理换行符：

#include <stdio.h>
#include <string.h>

struct Employee {
    int id;
    char name[50];
    float salary;
};

int main() {
    FILE *file;
    char filename[] = "employee.txt";
    int dataFound = 0;
    int recordno = 0;

    file = fopen(filename, "r+");
    if (file == NULL) {
        printf("Could not open file %s for reading and writing.\n", filename);
        return 1;
    }

    char name[15];
    printf("Enter the name of the employee to be updated: ");
    // 替换gets，用fgets读取并去掉末尾换行符
    fgets(name, sizeof(name), stdin);
    size_t len = strlen(name);
    if (len > 0 && name[len-1] == '\n') {
        name[len-1] = '\0';
    }

    struct Employee emp;
    while (fread(&emp, sizeof(emp), 1, file) == 1) {
        if (strcmp(emp.name, name) == 0) {
            dataFound = 1;
            printf("Enter the new details for employee %d:\n", emp.id);
            printf("Id: ");
            scanf("%d", &emp.id);
            printf("Salary: ");
            scanf("%f", &emp.salary);
            // 处理scanf遗留的换行符，避免影响后续读取
            while (getchar() != '\n');

            fseek(file, -sizeof(struct Employee), SEEK_CUR);
            if (fwrite(&emp, sizeof(struct Employee), 1, file) == 1) {
                printf("Employee details updated successfully.\n");
            }
            recordno++;
        }
    }

    if (dataFound == 0) {
        printf("\nData not found\n");
    }
    fclose(file);
    return 0;
}

方向2：改为文本方式读写（适配现有文件格式） #

直接解析文本文件的内容，用临时文件实现更新：

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

struct Employee {
    int id;
    char name[50];
    float salary;
};

int main() {
    FILE *file;
    char filename[] = "employee.txt";
    int dataFound = 0;
    char name[15];

    printf("Enter the name of the employee to be updated: ");
    fgets(name, sizeof(name), stdin);
    size_t len = strlen(name);
    if (len > 0 && name[len-1] == '\n') {
        name[len-1] = '\0';
    }

    file = fopen(filename, "r");
    if (!file) {
        printf("Could not open file %s for reading.\n", filename);
        return 1;
    }

    FILE *tempFile = fopen("temp.txt", "w");
    if (!tempFile) {
        printf("Could not create temp file.\n");
        fclose(file);
        return 1;
    }

    char line[100];
    struct Employee emp;
    while (fgets(line, sizeof(line), file)) {
        if (sscanf(line, "Id : %d", &emp.id) == 1) {
            fgets(line, sizeof(line), file);
            sscanf(line, "Name : %s", emp.name);
            fgets(line, sizeof(line), file);
            sscanf(line, "Salary : %f", &emp.salary);

            if (strcmp(emp.name, name) == 0) {
                dataFound = 1;
                printf("Enter the new details for employee %d:\n", emp.id);
                printf("Id: ");
                scanf("%d", &emp.id);
                printf("Salary: ");
                scanf("%f", &emp.salary);
                while (getchar() != '\n');
            }

            fprintf(tempFile, "Id : %d \n", emp.id);
            fprintf(tempFile, "Name : %s\n", emp.name);
            fprintf(tempFile, "Salary : %.1f \n", emp.salary);
        } else {
            fputs(line, tempFile);
        }
    }

    fclose(file);
    fclose(tempFile);

    remove(filename);
    rename("temp.txt", filename);

    dataFound ? printf("Employee details updated successfully.\n") : printf("\nData not found\n");
    return 0;
}

关键注意点 #

• 二进制读写与文本读写不能混用：fread/fwrite对应二进制文件，fscanf/fprintf/fgets对应文本文件。
• 禁止使用gets：该函数存在缓冲区溢出风险，必须用fgets替代，并手动处理输入末尾的换行符。

内容的提问来源于stack exchange，提问作者Aayush Pandey