更好的方式來讀取一個exec'd程序的stdout用C

Question

我使用管道讀取exec'd程序的stdout：

int pipes[2]; 
pipe(pipes); 
if (fork() == 0) { 
    dup2(pipes[1], 1); 
    close(pipes[1]); 
    execlp("some_prog", ""); 
} else { 
    char* buf = auto_read(pipes[0]); 
} 

從標準輸出讀，我有一個函數auto_read自動分配更多的內存如所須。

char* auto_read(int fp) { 
    int bytes = 1000; 
    char* buf = (char*)malloc(bytes+1); 
    int bytes_read = read(fp, buf, bytes); 
    int total_reads = 1; 
    while (bytes_read != 0) { 
     realloc(buf, total_reads * bytes + 1); 
     bytes_read = read(fp, buf + total_reads * bytes, bytes); 
     total_reads++; 
    } 
    buf[(total_reads - 1) * bytes + bytes_read] = 0; 
    return buf; 
} 

我之所以做這種方式是我不知道這個程序是多少文本要提前出局噴涌，我不希望創建一個過大的緩衝區，併成爲回憶豬。我想知道是否有：

1. 一個更清潔的方式來寫這個。
2. 這樣做的內存或速度更快的方式。

Answer 1

使用popen如果你只需要從一個進程來讀，並在* NIX平臺：

FILE *programStdout = popen("command", "r"); 

// read from programStdout (fread(), fgets(), etc.) 
char buffer[1024]; 

while (fgets(buffer, 1024, programStdout)) 
{ 
    puts(buffer); 
} 

編輯：你問了一個方法來映射一個節目輸出到文件，所以在這裏你去：

#import <stdio.h> 
#import <unistd.h> 
#import <sys/mman.h> 

void *dataWithContentsOfMappedProgram(const char *command, size_t *len) 
{ 
    // read the data 
    char template[] = "/tmp/tmpfile_XXXXXX"; 
    int fd = mkstemp(template); 

    FILE *output = fdopen(fd, "w+"); 
    FILE *input = popen(command, "r"); 

#define BUF_SIZ 1024 
    char buffer[BUF_SIZ]; 
    size_t readSize = 0; 
    while ((readSize = fread(buffer, 1, BUF_SIZ, input))) 
    { 
     fwrite(buffer, 1, readSize, output); 
    } 
    fclose(input); 

    input = NULL; 
#undef BUF_SIZ 

    // now we map the file 
    long fileLength = ftell(output); 
    fseek(output, 0, SEEK_SET); 

    void *data = mmap(NULL, fileLength, PROT_READ | PROT_WRITE, MAP_FILE | MAP_PRIVATE, fd, 0); 

    close(fd); 

    if (data == MAP_FAILED) 
     return NULL; 

    return data; 
} 


int main() 
{ 
    size_t fileLen = 0; 
    char *mapped = dataWithContentsOfMappedProgram("echo Hello World!", &fileLen); 

    puts(mapped); 

    munmap(mapped, fileLen); 
}