程序代码：

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

char *readLine(FILE *file){
    if(file == NULL){
        exit(1);
    }
    /* malloc linebuffer */
    int baseLen = 256;  // 初始长度设置256字符
    char *lineBuf = (char *)malloc(sizeof(char) * baseLen);
    if(lineBuf == NULL){
        exit(1);
    }

    int ch,index=0;
    while((ch=fgetc(file)) != 10 && ch != EOF){ // ASCII 10 => "\n"
        lineBuf[index] = ch;
        index++;

        if(index == baseLen){
            baseLen += 256;
            lineBuf = (char *)realloc(lineBuf, baseLen); // 内存不足时每次再重新分配256字符空间
            if(lineBuf == NULL){
                exit(1);
            }
        }
    }
    lineBuf[index] = '\0'; // end of string add '\0'

    return lineBuf;
}

int main(int argc, char *argv[])
{
    FILE *fp = fopen(argv[1],"r");
    if(fp == NULL){
        exit(1);
    }
    while(!feof(fp)){
        char *line = readLine(fp);
        printf("%s\n",line);
    }
    exit(0);
}

程序代码：

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

char* readline( FILE* file )
{
    const size_t baselen = 256;
    char* line = NULL;
    size_t size = 0;
    size_t capacity = 0;

    for( ; ; )
    {
        if( capacity <= size+1 )
        {
            capacity += baselen;
            char* t = realloc( line, capacity );
            if( !t )
            {
                free( line );
                return NULL;
            }
            line = t;
        }

        {
            char* t = fgets( line+size, capacity-size, file );
            if( t == NULL )
            {
                if( ferror(file) )
                {
                    free( line );
                    return NULL;
                }
                return size!=0 ? line : NULL;
            }
        }

        {
            size_t t = strlen( line+size );
            if( t!=0 && line[size+t-1]=='\n' )
            {
                line[size+t-1] = '\0';
                break;
            }
            size += t;
        }
    }

    return line;
}

int main( void )
{
    FILE* fp = fopen( "d:/test.txt", "r" );
    for( char* line; line=readline(fp), line; )
    {
        puts( line );
        free( line );
    }
}

[此贴子已经被作者于2020-11-9 13:21编辑过]

[此贴子已经被作者于2020-11-9 14:14编辑过]